2 sticks (1 cup) unsalted butter, softened1 pound sharp cheddar, coarsely grated (preferably in a food processor; 5 cups)1 large egg yolk1/4 teaspoon Dijon mustard2 tablespoons dry mustard1/4 cup brown or yellow mustard seeds (we reduced to 2 tablespoons, which worked fine)2 teaspoons salt2 cups all-purpose flour, plus more for surface
Makes about 4 dozen.
Blend butter, cheese and egg yolk in a food processor until smooth. Add mustards, salt and flour and pulse just until combined. Transfer the soft dough to a bowl. Cover and chill 15 minutes.
Halve the dough and shape each half into a 12-inch log on a lightly floured surface. Wrap in wax paper and foil, chill until firm, at least 4 hours. (Dough can be frozen for several months. Defrost in the refrigerator before slicing.)
Place oven racks in upper and lower thirds of the oven and preheat to 350 degrees. Line 2 baking sheets with parchment paper (or nonstick baking mat, such as Silpat). Unwrap logs and cut into 1/8-inch-thick slices with a sharp knife. Place slices on baking sheet about 1 inch apart.
Bake until lightly brown around edges, switching position of pans halfway through baking, 12 to 15 minutes. Cool on a rack. Cool crackers and store in an airtight container.