For the biscuits:
Preheat the oven to 400˚ F. Line a baking sheet with a silicone baking mat or parchment paper. In a medium bowl, combine the flour, baking powder, and salt. Whisk to blend. Stir in the pieces of butter and toss to coat in the dry ingredients. Using two forks or a pastry cutter, cut the butter into the dry ingredients until the mixture is coarse largest butter chunks are the size of small peas. Stir in the cheddar and diced jalapeños and toss briefly to combine. Pour in the milk and stir gently with a fork until a sticky dough has formed.
Turn the mixture out onto a well floured work surface. Don’t worry if the dough has some dry bits. Briefly knead until the dough is mostly cohesive and no longer sticky, being careful not to overwork it. Form the dough into a square slab about 7 x 7″. Use a sharp kitchen knife and cut into thirds in one direction, and then the other to form 9 square biscuits.* Transfer the biscuits to the prepared baking sheet and brush the tops of the biscuits lightly with the melted butter.
Bake for about 18 minutes, rotating the pan halfway through baking, until the tops are golden and the biscuits are baked through. Transfer to a wire rack and let cool slightly before serving. Serve as desired with salsa, avocado and eggs.
*At this point, the unbaked biscuits can be frozen. When ready to bake, simply bake directly from the freezer as directed above and add a few minutes onto the baking time (no need to thaw first.)