Preheat your oven to 425°F with a rack in the upper portion. 

Mix together the flour, salt, baking powder, and sugar.

Work the butter into the flour mixture using your fingers, a fork or pastry blender, a stand mixer, or a food processor; your goal is an evenly crumbly mixture (think breadcrumbs).

Drizzle the smaller amount of milk evenly over the flour mixture. Mix quickly and gently for about 15 seconds, until you've made a cohesive dough. If the mixture seems dry and won't come together, don't keep working it; drizzle in enough milk — up to an additional 2 tablespoons to make it cohesive.

Place the dough on a lightly floured work surface. Pat it into a rough rectangle about 3/4" thick. Fold it into thirds like a letter and roll gently with a floured rolling pin until the dough is 3/4" thick again.

Cut the dough into biscuits.

Place the biscuits bottom side up on your prepared baking sheet; turning them over like this yields biscuits with nice, smooth tops. Brush the biscuits with milk, to enhance browning.

Bake the biscuits for 15 to 20 minutes, until they're lightly browned. Remove them from the oven, and serve warm.

Store any leftover biscuits, well wrapped, at room temperature for several days. Freeze for longer storage. Biscuits are always best when they're rewarmed before serving.