01 - Pulse flour, salt, cayenne pepper, and black pepper in food processor until evenly mixed.
02 - Add cold diced butter and pulse until mixture resembles coarse crumbs.
03 - Add grated cheddar and pulse just until dough comes together. Add 1-2 teaspoons cold water if mixture is too crumbly.
04 - Turn dough onto parchment paper and shape into 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 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.