01 - In a food processor, pulse the flour, salt, cayenne, and black pepper until combined.
02 - Add the cold butter and pulse until the mixture resembles coarse crumbs.
03 - Add the grated cheddar and pulse just until the dough comes together. If the dough is too crumbly, add 1–2 teaspoons of cold water as needed.
04 - Turn the dough out onto a sheet of parchment paper. Shape into a log about 1 1/2 inches in diameter. Wrap tightly and refrigerate for at least 1 hour, or until firm.
05 - Preheat the oven to 375°F. Line a baking sheet with parchment paper.
06 - Slice the chilled dough into 1/4-inch rounds and arrange on the prepared baking sheet, spacing them 1 inch apart.
07 - Sprinkle with poppy seeds or sesame seeds if desired.
08 - Bake for 12–15 minutes, or until golden at the edges.
09 - Cool on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely.