Preheat oven to 400 degrees
Place flour, baking powder, salt and butter in a food processor and pulse until the mixutre resembles course crumbs. You can also use a pastry blender to cut the butter into the dry ingredients if you don't have a food processor.
Transfer the flour mixture to a large bowl and stir in the sugar, rhubarb and strawberries
Add the milk and stir just until combined. If it feels too dry you can add an extra tablespoon of milk at a time. The dough should feel a bit sticky when you turn it onto the counter.
Dump the dough onto a well floured counter top, then dust the top of the dough generously with flour.
Bring the mixture together with your hands and flatten out to a 10 inch circle. If it is sticky as you flatten it you can dust with a bit more flour.
With a sharp knife, cut the dough into 8 wedges, then transfer to a parchement lined baking sheet. If you don't have parchement paper, a baking sheet sprayed with non-stick spray will work as well.
In a small bowl, whisk egg and water and brush on top of the scones
Bake for approximately 20 minutes until scones are golden brown then remove from the oven and transfer to a cooling rack.
When scones are almost cool, drizzle with icing and serve