Preheat oven to 425 degrees F. Grease a baking pan.
Cook and drain sausage.
In a large bowl, whisk together the flour, baking powder, baking soda, and salt.
Add the butter and, using a pastry cutter, fork, or your fingers, cut the butter into the dry ingredients until the mixture has pea-sized crumbs. Stir in the sausage and cheese (and green onions if you're adding them.)
Add the buttermilk and combine. I find it easiest to use a fork to gently stir the mixture until all of the dry ingredients are moistened. Then, use your hands to knead the mixture a few times in the bowl to bring the dough together.
Turn the dough out onto a parchment-lined counter and pat into an 8x10-inch rectangle. Cut the dough into 12 squares.
Transfer the biscuits to the baking pan, leaving 1-inches between each biscuit. Brush the tops of each biscuit with the melted butter.
Bake until the biscuits are golden brown, about 18 to 20 minutes.