Pickled Beef Tongue, Leek-Sweet Onion Purée, and Pickled Mustard Seeds
For the Pickled Mustard Seeds:
In a large saucepot, combine the mustard seeds, vinegar, chilis, and garlic and bring to a boil. Remove from the heat and pour into a 1-quart container. Seal and let sit for 7 days.
For the Pickled Beef Tongue:
Rinse the tongue under cold water. Combine the water, vinegar, mustard seeds, coriander, chili flakes, peppercorns, and kosher salt in a sealable container. Refrigerate for 2 days. Pre-heat the oven to 325°F. Add the tongue and brine to a Dutch oven; cook 6 to 7 hours, until tender. Remove from the liquid, cool, and slice into ½-inch slices.
For the Leek-Sweet Onion Purée:
In a large saucepan, sauté the onions, garlic, and leeks with 3 tablespoons of butter until translucent. Season with salt and pepper. Add ingredients to blender and purée with 4 tablespoons cold butter.
To Assemble and Serve:
Warm the Pickled Beef Tongue. Plate a swipe of Leek-Sweet Onion Purée. Fan out 3 slices of warm Pickled Beef Tongue. Top the tongue with 1 teaspoon Pickled Mustard Seeds.