Mix lemon juice with milk. Stir and let it sit for 5 - 10 minutes in the refrigerator. This mixture is the buttermilk.
Preheat the oven to 450F.
Put the dry ingredients in the food processor. Pulse several times to mix. Add the butter cubes.
Pulse until the pieces are no bigger than peas.
Add buttermilk and pulse until dough comes together.
Lightly dust with flour the working surface and knead gently about 3-4 times to bring it together.
Roll the dough into a 9x5-inch rectangle and about 1/2-inch thick.
Fold the dough into thirds like a business letter.
Repeat this step, roll the dough into a 9x5-inch rectangle about 1/2-inch thick, and again fold it into thirds like a letter.
Finally roll the dough out to 3/4-inch thickness. Using a round cutter, cut biscuits from the dough (don't twist the cutter, use a straight up and straight down motion).
Transfer to the prepared baking sheet, leaving about 1 inch of space between them.
Brush the biscuits with melted butter.
Bake for about 11-12 minutes. Transfer the biscuits to a wire rack to cool for a few minutes and serve warm.
