Preheat oven to 400°F. Line baking sheet with parchment paper and set aside.
In a large bowl, whisk together the flour, baking powder, baking soda, and salt. Cut in the chilled butter using a pastry blender (or two forks or your fingers) until the flour mixture resembles crumbly, course sand. Cut in the shortening.
Pour in the cold buttermilk. Use a sturdy rubber spatula to fold the mixture together until a dough forms. The dough will look sticky.
Turn the dough out onto a lightly floured work surface. Lightly dust your hands with flour. Knead the dough together until almost smooth. Pat the dough until 1-inch in thickness. Use a 3-inch round cutter to punch biscuits. Gather any remaining dough and knead together to cut more biscuits. You will end up with 4 biscuits.
Bake for 15 to 18 minutes until the biscuits are golden brown on top.
GRAVY
While the biscuits are baking, prepare the sausage gravy. Place a large skillet over medium high heat. Add the sausage meat. Using a spatula, break the sausage into small pieces. Cook for about 5 minutes until the sausage has browned and there are no longer any bits of pink.
Reduce the heat to medium. Add the flour and stir to combine. Keep stirring until the meat has absorbed the flour and there are no longer any dry streaks of flour.
Slowly add the milk. Bring the mixture to a simmer to thicken the gravy. Cook for about 5 minutes. If the gravy is too thick, add the milk 1 tablespoon at a time until desired consistency is achieved. Taste the gravy and season with salt and pepper, as needed.
Slice warm biscuits in half and place in a serving plate. Ladle hot sausage gravy over biscuits.
Notes
Bulk breakfast sausage usually is packaged in small plastic tubes. Bulk sausage refers to sausage without any casing. It often comes in "spicy/hot" or "mild/regular" flavors.