Start by preheating your oven to 400°F (200°C). This ensures that your biscuits will bake evenly and achieve that perfect golden brown color.

In a large mixing bowl, combine the self-rising flour, baking powder, baking soda, sea salt, and granulated sugar. Mix well so that everything is evenly distributed. Next, add in the diced cold butter. Use a pastry cutter or your fingers to work the butter into the flour mixture, which should resemble coarse crumbs.

In another bowl, whisk together the buttermilk, large egg, vanilla extract, and lemon zest. Pour this mixture into the dry ingredients. Stir until just combined—be careful not to overmix! Gently fold in the fresh blueberries. It’s okay if some berries burst; that just adds to the flavor.

Turn the dough out onto a lightly floured surface. Gently knead it just until it comes together. Pat the dough into a ¾-inch thick rectangle. Cut out rounds using a biscuit cutter and place them on a lined baking sheet, leaving some space between each biscuit.

In a small bowl, whisk the egg yolk with a splash of water. Brush this mixture over the tops of the biscuits. This will give them that lovely sheen when baked.

Place the baking sheet in the oven and bake for 15-20 minutes or until golden brown. Keep an eye on them—nothing worse than overbaked biscuits!

While the biscuits are in the oven, melt the butter in a small bowl. Whisk in the powdered sugar, lemon juice, and buttermilk until smooth. Once the biscuits cool slightly, drizzle the glaze on top.