01 - Pulse flour, salt, cayenne, and black pepper in food processor until thoroughly combined.
02 - Add cold diced butter and pulse until mixture resembles coarse crumbs with small butter pieces visible.
03 - Add grated cheddar and pulse just until dough comes together. Add 1-2 teaspoons cold water only if dough remains crumbly.
04 - Turn dough onto parchment paper and shape into a 1 1/2-inch diameter log. Wrap tightly and refrigerate minimum 1 hour until firm.
05 - Preheat oven to 375°F and line baking sheet with parchment paper.
06 - Slice chilled dough into 1/4-inch rounds and arrange on prepared baking sheet with 1-inch spacing between pieces.
07 - Sprinkle poppy seeds or sesame seeds over rounds if desired.
08 - Bake 12-15 minutes until edges turn golden brown.
09 - Let coins rest on baking sheet 5 minutes, then transfer to wire rack to cool completely.