Preheat your oven to 400°F (200°C). Line a baking sheet with parchment paper; this helps prevent sticking and makes cleanup a breeze. In a large mixing bowl, whisk together the flour, 1/4 cup granulated sugar, baking powder, and salt until well combined.

Add the very cold, cubed butter to the dry ingredients. Using a pastry blender, two knives, or your fingertips, cut the butter into the flour mixture until it resembles coarse crumbs with some pea-sized pieces of butter still visible. The colder your butter, the flakier your biscuits will be!

Gently fold in the fresh blueberries. Make a well in the center of the mixture and pour in the very cold buttermilk. Mix with a spoon or your hands just until the dough comes together. Be careful not to overmix; a shaggy, slightly sticky dough is perfect.

Turn the dough out onto a lightly floured surface. Gently pat the dough into a roughly 1-inch thick rectangle. Fold the dough in half, then pat it down to about 3/4-inch thick. Repeat this folding and patting process 1-2 more times; this layering helps create those amazing flaky biscuit layers.

Using a 2.5-inch round biscuit cutter, press straight down into the dough without twisting. Twisting seals the edges and can prevent a good rise. Gather the scraps, gently pat them together, and cut any remaining biscuits. You should get about 8-9 biscuits.

Place the cut biscuits on your prepared baking sheet, leaving about 1 inch between them. Brush the tops of the biscuits lightly with whole milk or heavy cream, then sprinkle them with the remaining 1 tsp of granulated sugar. This will give them a lovely golden crust and a sweet sparkle.

Bake for 15-18 minutes, or until the tops are golden brown and a wooden skewer inserted into the center comes out clean. Let them cool on the baking sheet for a few minutes before transferring to a wire rack. Serve warm with butter, jam, or just as they are!