Preheat your oven to 375°F.

In a large bowl, combine flour, sugar, baking powder, baking soda, and salt.

Add the chilled butter chunks and use your hands or a pastry blender to work them into the flour until they're the size of currants.

Fold in the diced strawberries and rhubarb.

Whisk together the buttermilk and egg yolk, then gradually add it to the flour mixture.

Transfer the dough to a floured surface and gently knead it until it forms a ball.

Flatten the dough into a 7-inch disk, then cut it into wedges. Place the wedges on a parchment-lined baking sheet and brush them with the separated egg white.

Bake for 18-25 minutes or until they turn slightly golden. Once baked, let them cool on a wire rack.

For the glaze, mix powdered sugar with milk one teaspoon at a time until it reaches your desired consistency. Drizzle the glaze over the cooled scones.