Blend together the Unsalted Butter (2 stick), Sharp Cheddar Cheese (1 pound) and Large Egg Yolks (1) in the food processor until smooth.
Combine the Dijon Mustard (3 tablespoon), Dry Mustard (2 tablespoon) and Mustard Seeds (1/4 cup) in a small bowl and stir. Add to the butter mixture.
Combine the Salt (2 teaspoon), Cayenne Pepper (1/2 teaspoon) and All-Purpose Flour (2 cup) in a bowl and whisk to combine. Add the dry ingredients to the butter mixture. Put the lid on the food processor and pulse until a soft dough forms.
Add the Pecans (1/2 cup) and pulse 2-3 more times until combined. Refrigerate dough for 15 minutes.
Divide the dough into equal portions (2, 3, or 4). Shape and roll the dough into 10" logs. Roll the dough in wax or parchment paper and refrigerate for at least 4 hours or until firm before continuing.
Position oven racks in upper and lower thirds of the oven and preheat to 350 degrees F (180 degrees C). Line baking sheets with parchment paper.
Unwrap logs and cut into slices with a very sharp knife into 1/8" thick rounds. Arrange 1" apart on the baking sheet.
Bake in batches, switching positions of the pans halfway through the baking process. Cook a total of 12-15 minutes until lightly golden. Transfer crackers to racks to cool.
Store crackers in an airtight container for up to a week.