Place the beef tips, diced onion, minced garlic, cracked peppercorns, beef broth, Worcestershire sauce, and 1/2 teaspoon salt in the slow cooker. Stir to combine.
Cover and cook on low for 7 hours until the beef is fork-tender.
In a small bowl, whisk the 2 tablespoons flour with 1/4 cup of the cooking liquid until smooth. Stir the mixture back into the slow cooker and cook on high for 20 minutes to thicken the gravy.
While the gravy thickens, preheat the oven to 425 degrees. In a mixing bowl, combine the 2 cups flour, baking powder, baking soda, and 1/2 teaspoon salt. Cut in the cold butter until the mixture resembles coarse crumbs.
Stir in the buttermilk until a soft dough forms. Drop spoonfuls onto a baking sheet and bake for 12 to 15 minutes until golden.
Spoon the peppercorn beef tips and gravy over the warm biscuits to serve.