How to Make It
In a food processor, combine the flour, baking powder, salt and baking soda and process until blended. Add the cold butter, Cheddar and rosemary and pulse until the mixture resembles coarse meal. Gradually pulse in the milk until the dough just comes together. Turn the dough out onto a lightly floured work surface and knead gently. Shape the dough into a flat disk, wrap in plastic and refrigerate until firm, about 1 hour.
Preheat the oven to 375°. On a lightly floured surface, roll out the dough 1/3 inch thick. Using a 3-inch biscuit cutter, cut out 8 biscuits. Transfer the biscuits to a baking sheet, brush with melted butter and bake for about 20 minutes, or until golden. Slice the biscuits in half, fill with the blue cheese and sausage and serve.