Preheat your oven to 375°F and lightly grease a baking sheet. Cut the chilled butter into ½-inch cubes and return to the refrigerator until needed—cold butter is essential for creating tender, flaky scones. Hull and chop the strawberries into ½-inch pieces, and have the blueberries ready. Sift the powdered sugar into a small bowl to remove any lumps for a smoother glaze later.

In a large bowl, whisk together the flour, baking powder, baking soda, salt, and sugar. This combines your leavening agents evenly throughout the flour, ensuring consistent rise and texture in every scone. Make sure there are no lumps of baking powder or soda hiding in the mixture.

Add the chilled butter cubes to the dry ingredient mixture and use a pastry cutter, two knives, or your fingertips to work the butter into the flour until the mixture resembles coarse breadcrumbs with some pea-sized pieces of butter remaining. I find using my fingertips gives me the best control to keep everything cold while creating the right texture—work quickly so the butter doesn't warm up, as this keeps the scones tender and flaky rather than tough and dense.

Gently fold the chopped strawberries and blueberries into the crumbly mixture using a rubber spatula or wooden spoon—handle the fruit carefully to avoid crushing it. In a separate small bowl, whisk together the egg, sour cream, milk, and vanilla extract until well combined. Pour the wet mixture into the dry ingredients and gently fold until just combined—do not overmix, as overworking the dough will develop gluten and make the scones tough. A few lumps are okay; I actually prefer slightly undermixed dough for the most tender, flaky scones.

Turn the dough out onto a lightly floured work surface and gently knead it just 2-3 times to bring it together—don't overwork it. Shape it into an 8-inch circle about ¾ inch thick, then use a sharp knife to cut it into 8 wedges like a pie. Transfer the wedges to the prepared baking sheet, spacing them about 2 inches apart to allow for even baking.

Bake for 15-18 minutes, until the scones are golden brown on top and a toothpick inserted into the center comes out clean. Remove from the oven and transfer the scones to a wire cooling rack. Let them cool for about 10 minutes before adding the glaze—this gives them just enough time to set slightly while still warm enough to absorb the lemon glaze beautifully.

While the scones cool, whisk together the sifted powdered sugar and lemon juice until smooth and pourable. Drizzle the glaze over the warm scones, allowing it to pool slightly on top and drip down the sides. Serve warm or at room temperature.