01 - Pulse the flour, salt, cayenne pepper, and black pepper in a food processor until evenly combined.
02 - Add cold diced butter to the processor and pulse until mixture resembles coarse crumbs.
03 - Add grated cheddar and pulse just until dough forms. Add 1-2 teaspoons cold water if dough is too crumbly to hold together.
04 - Shape dough into a 1 1/2-inch diameter log on parchment paper. Wrap tightly and refrigerate for at least 1 hour until firm.
05 - Preheat oven to 375°F. Line a baking sheet with parchment paper.
06 - Cut chilled dough into 1/4-inch thick rounds and arrange on prepared baking sheet, leaving 1 inch of space between each coin.
07 - Sprinkle with poppy seeds or sesame seeds if desired.
08 - Bake for 12-15 minutes until edges are golden brown.
09 - Let cool on baking sheet for 5 minutes, then transfer to wire rack to cool completely.