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