01 - Pulse flour, salt, cayenne, and black pepper in food processor until combined.
02 - Add cold butter to processor and pulse until mixture resembles coarse crumbs.
03 - Add grated cheddar and pulse until dough comes together. Add 1-2 teaspoons cold water if too crumbly.
04 - Shape dough into 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 baking sheet with parchment paper.
06 - Slice chilled dough into 1/4-inch rounds. Arrange on prepared baking sheet 1 inch apart.
07 - Sprinkle with poppy seeds or sesame seeds if desired.
08 - Bake for 12-15 minutes until golden at edges.
09 - Cool on baking sheet for 5 minutes, then transfer to wire rack to cool completely.