Preheat the oven to 400 F.
Sift together the flour, baking powder, and salt into a large bowl.
Mix the milk and vinegar together and set aside for at least five minutes. This sour milk makes the scones soft and moist.
Grate the butter using a box grater into the dry ingredients. Combine with the flour either using your fingers, a fork, or a pastry cutter. The butter should now be in about pea-sized bits.
Add the jalapeños and cheese and mix.
Add the sour cream and the sour milk and mix everything together until it forms a shaggy dough.
Pat the dough out on a clean surface until it is about 1 inch thick.
Cut the dough using a 2-inch circular cutter and place them onto a parchment lined baking sheet.
Brush the tops of the scones with the beaten egg.
Bake the scones for 20 to 25 minutes, or until the tops are golden brown.