- 2 sticks (1 cup) unsalted butter, softened
- 1 lb sharp Cheddar, coarsely grated (preferably in a food processor; 5 cups)
- 1 large egg yolk
- 1/4 teaspoon Dijon mustard
- 2 tablespoons dry mustard
- 1/4 cup brown or yellow mustard seeds
- 2 teaspoons salt
- 2 cups all-purpose flour plus additional for dusting
- Special equipment: parchment paper
- Blend together butter, cheese, and yolk in a food processor until smooth. Add remaining ingredients and pulse until just combined. (If you have a small processor, divide butter mixture after blending and pulse with remaining ingredients in 2 batches.) Transfer dough (it will be very soft) to a bowl and chill, covered, 15 minutes.
- Halve dough, then shape each half into a 12-inch log on a lightly floured surface. Wrap logs in wax paper and foil, then chill until firm, at least 4 hours.
- Put oven racks in upper and lower thirds of oven and preheat oven to 350°F. Line 2 large baking sheets with parchment paper.
- Unwrap logs and cut into 1/8-inch-thick slices with a sharp thin knife, then arrange slices about 1 inch apart on baking sheets. Bake in batches, switching position of sheets halfway through baking, until pale golden, 12 to 15 minutes. Transfer crackers to racks to cool, about 5 minutes. Line sheets with clean parchment between batches.