Chocolate Rugelach

To the bowl of a KitchenAid Commercial stand mixer fitted with a paddle, add yeast mixture, vanilla, egg yolk, and sour cream followed by salt, sugar, and flour. On speed 1, mix for 3 minutes. Increase to speed 2, add butter, allowing each cube to combine with the mixture before adding the next. When butter is combined, mix 2 minutes more, until dough is silky smooth. Into a greased rectangular container, press dough; cover and refrigerate at least 4 hours or overnight. Onto a clean work surface, turn dough out and press into an even block. Using a pasta roller and working quickly, flatten until dough has passed through setting 1. Cut dough into two 6-inch strips. On 1 strip, evenly spread chocolate filling to coat. Lay the other strip atop the chocolate covered strip. Cut into 2¼-inch-wide triangles, roll into crescent shapes, and arrange on a sheet tray in tight rows. Proof 30 minutes to 1 hour, until soft to the touch. Heat oven to 325°F. Brush Rugelach with egg wash and bake 20 to 25 minutes. While hot, glaze while simple syrup.