Tips: Two soft, cakelike cookies enclose a creamy filling in these popular goodies. The cookie dough chills overnight before you bake it; the base for the filling, which should be cold when used, can also chill overnight. These are stored in the fridge or freezer, but I think they taste best if brought to room temperature before eating. The coffee in the filling can be omitted if you wish. These are a project, but a gratifying one. Make sure you read the recipe all the way through before making these, and check out the filling variation at the end of the recipe.

• 2 cups plus 2 Tbsp. plus 2 tsp. all-purpose flour
• 1/3 cup unsweetened Dutch process cocoa powder
• 1-1/8 tsp. baking powder
• 3/8 (1/4 plus 1/8) tsp. baking soda
• Pinch salt
• 2/3 cup unsalted butter, softened
• 3/4 cup granulated sugar
• 2/3 cup firmly packed light brown sugar
• 1 tsp. vanilla
• 2 eggs, graded "large"
• 2/3 cup sour cream

• 1/3 cup plus 1 tsp. sifted all-purpose flour
• 1 cup whole milk
• 1 cup unsalted butter, divided
• 2-1/2 tsp. instant coffee
• Pinch salt
• 2-3/4 cups sifted or strained confectioners' sugar
• 1 tsp. vanilla

For Cookie Dough: Sift together flour, cocoa powder, baking powder, baking soda, and salt. Set aside.

In large bowl of electric mixer, combined softened butter, sugars, and vanilla. Beat at medium speed for a minute or two, until well-combined and fluffy. (Scrape bowl and beater(s) with rubber spatula as necessary throughout mixing to ensure thorough blending of ingredients.) Add eggs one at a time, beating well after each. At lowest speed, add sifted dry ingredients in thirds and sour cream in halves, beginning and ending with dry ingredients and beating after each addition just until incorporated. Remove from mixer. If you wish, scrape dough into a medium bowl. Cover top of bowl with a layer of paper towelling, then cover tightly with aluminum foil (the paper towel will absorb any condensation that forms before it can drip into the dough). Chill overnight.

Next day, adjust rack to center of oven. Preheat oven to 350 degrees F. Line cookie sheets with aluminum foil cut to fit; grease foil lightly with vegetable shortening (I've tried baking these cookies on parchment paper, but lightly greased foil works better). Have ready nonstick cooling racks and a nonstick metal spatula with a broad blade (or spray regular cooling racks and a regular broad-bladed metal spatula very lightly with nonstick cooking spray). Using a heaping tablespoonful of dough for each cookie and keeping shapes as round as possible, bake 2 or 3 "test" cookies. Make sure you leave room between them; these spread as they bake. Bake10-12 minutes, or just until a toothpick inserted into the center of a cookie emerges with only a few moist crumbs clinging to it. Do not overbake.

Continue forming and baking the cookies; I place only 12 mounds of dough on a 15-1/2" by 10-1/2" baking sheet. Form a sheet or two of unbaked cookies, then, while they bake, replace the remaining dough in the refrigerator. This dough is somewhat difficult to work with, but it handles a bit more easily when cold. Bake only one sheet of cookies at a time. Allow baked cookies to stand on sheets for 2 minutes before removing to prepared cooling racks. You'll need to scrape off the broad-bladed spatula after removing every other cookie or so from the sheet; I use the back of a flat knife for this. Cool the cookies completely, then store airtight WITH WAX PAPER BETWEEN THE COOKIE LAYERS IN THE STORAGE CONTAINER. Do not omit the wax paper, even if you're only going to store the cookies for a short while before filling them. Note, incidentally, that it is best to fill the cookies within an hour or two of storing them. They can wait a while longer, but they'll start to become limp. You'll have about 48 cookies.

For Filling: Set out 2 Tbsp. of the butter near stovetop (reserve and refrigerate remainder). Place sifted flour in heavy-bottomed, one quart pot. Very gradually, whisk in the milk, making the mixture as smooth as possible (there will still be some lumps--OK). Cook over medium heat, whisking constantly, until mixture boils. Reduce heat; simmer 5 minutes, stirring constantly with whisk. Mixture will be very stiff and probably somewhat lumpy--OK. Remove from heat. Immediately add instant coffee and salt and whisk in. Add the 2 Tbsp. butter and stir with whisk until melted. If the mixture has any lumps (mine always does), strain through a fine strainer into a small bowl, pressing through as much as possible. Immediately cover with plastic wrap that has a few small holes pierced through it, placing the plastic wrap right on the surface of the mixture to prevent a skin from forming. Cool briefly, then chill until cold or overnight.

When ready to complete filling, soften reserved butter (do not melt) and place in large bowl of electric mixer (fitted with paddle beater, if available).

At medium speed, beat butter until smooth. Add 1 cup of the confectioners' sugar and the vanilla. Beat at a low speed to incorporate. Add another cup of the sugar; beat to incorporate, then beat at medium speed until fluffy. Stir the cold milk-flour mixture to loosen it (it will be very stiff). By large spoonfuls, add milk-flour mixture, beating at low speed to incorporate (filling may look slightly curdled--OK), then at medium speed until smooth. Finally, add remaining 3/4 cup confectioners' sugar; beat at medium speed just until fluffy and well-mixed. If room is very warm, chill filling for about 20 minutes. It should be fluffy and light-textured, but not runny.

Just before you're ready to fill the cookies, lay out several long sheets of wax paper on a flat work surface. Place cookies, flat side up, on wax paper. Try to pair up cookies that are approximately the same size and shape. Place a very heaping teaspoon of filling on the flat side of one cookie in each pair, then sandwich the pairs, flat sides together. Very gently flatten slightly so filling comes just to the edge of the cookie sandwiches (if you presstoo hard, the filling will squish out and your hand will stick to the top of the cookie sandwich).

Wrap each cookie sandwich tightly in plastic wrap. Store in refrigerator for up to a few days (freeze for longer storage). Allow cookies, still in wrapping, to come to room temperature before eating, if desired.

About 2 dozen sandwiches

Variation: Cookie Ice Cream Sandwiches

Make cookies as above, but omit filling. Instead, use a favorite, good-quality ice cream that isn't rock-hard at freezer temperature (I like to use Starbucks). You'll need about 2 quarts of ice cream.

Place a wax-paper-lined cookie sheet in the freezer (do NOT omit this step, or the cookieswill stick to the cookie sheets). Lay cookies out in pairs on other wax paper sheets on flat surface as described above. Working quickly, place a scoop of ice cream (about 1/3 cup) on top of one cookie in a pair. Sandwich the two cookies, flat sides together. Now, place a piece of wax paper on top of the sandwich, and press down to flatten so that the ice cream comes just to the edge (you MUST use wax paper here, or the cookie will stick to your hand and tear). I make one sandwich at a time and transfer each to the lined sheets in the freezer as it's completed.

Freeze for an hour or two, then wrap each sandwich tightly in plastic wrap. Once these are frozen and wrapped, they can be stored in a freezer bag, if you wish. Remove from freezer just before serving. Great with warmed hot fudge sauce!

About 2 dozen sandwiches

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