In a large mixing bowl, whisk together the flour, baking powder, salt, and mixed seeds.

Cut in the cold butter using a pastry blender or your fingertips until the mixture resembles coarse crumbs.

Gradually add the cold buttermilk, mixing until just combined. Do not overmix.

Turn the dough out onto a lightly floured surface and gently pat it into a 1-inch thick rectangle. Use a biscuit cutter or knife to cut out biscuits.

Place the biscuits on a baking sheet lined with parchment paper and bake in a preheated oven at 400°F (200°C) for 15-20 minutes, or until golden brown.

Let the biscuits cool slightly before serving.