Preheat your oven to 425°F (220°C). Lightly grease a baking sheet or line it with parchment paper.

In a large mixing bowl, add the self-rising flour and sugar (if using). Whisk to combine.

Add the cold, cubed butter to the flour mixture. Using a pastry blender, two knives, or your fingertips, cut the butter into the flour until the mixture resembles coarse crumbs with some pea-sized pieces of butter remaining. This step is crucial for flaky biscuits.

Gradually pour in the cold milk, stirring gently with a fork until just combined. Be careful not to overmix; the dough should be shaggy and slightly sticky.

Turn the dough out onto a lightly floured surface. Gently knead it a few times (about 5-6 turns) to bring it together. Pat or gently roll the dough into a 3/4-inch thick rectangle.

Fold the dough in half, then pat or roll it out again to 3/4-inch thickness. Repeat this folding and patting process 2-3 more times. This creates layers for flakiness. Do not overwork the dough.

Using a biscuit cutter or a glass rim (about 2-3 inches in diameter), cut out the biscuits. Press straight down without twisting to ensure even rising.

Place the biscuits onto the prepared baking sheet, ensuring they are touching each other for softer sides, or spaced apart for crispier edges.

Bake for 12-15 minutes, or until the biscuits are golden brown and have risen beautifully. For an extra sheen and flavor, brush the tops with melted butter immediately after they come out of the oven.

Let cool slightly on the baking sheet before serving.