Preheat oven to 400°F. Grease a baking sheet or line with parchment paper. Mix eggs and buttermilk in a small bowl and set aside. Place baking mixture in a large bowl. Using a fork or pastry blender, cut in cold butter until it is the size of small peas. Add egg mixture to dry ingredients with optional add-ins and mix until evenly moistened. Invert mixture onto gluten-free floured surface and knead briefly to form dough. Pat dough to 1 inch thick. Fold dough in half and pat again to 1 inch thick. Repeat folding and patting twice more. Cut out cookies and transfer to baking sheet. Brush top of each biscuit with melted butter, if desired. Bake until golden brown, about 20 minutes. Makes 8 cookies.
Sweet biscuit variation: Add 3 tablespoons granulated sugar to mix. Brush biscuits with milk and sprinkle with glitter sugar before baking.