Preheat oven to 400°. Line a baking sheet with parchment paper. If you don't have parchment paper, spray your baking sheet well.
In a large bowl, mix together all dry ingredients and lime zest. Using your fingers, pastry cutter or fork, quickly work in the butter until it resembles coarse meal or small pebbles. Don't handle the butter too much or it'll melt!
In a small bowl, beat the egg until almost frothy. Add egg to dry mixture, and slightly mix in with a fork. Then begin adding milk, starting with 3/4 Cup. Mix only until most of the flour incorporated. Add in berries, and mix in only until incorporated.
Test your dough! Pull a small handful out and squeeze it together If it holds together and is slightly sticky, do not add more milk. If it crumbles and doesn't hold together, add milk just a tablespoon at a time until dough holds together.
Turn dough out on lightly floured surface. Pat into a circle, then gently roll out to 1" thickness. Using a sharp knife, bench scraper or pizza cutter, cut the circle into 8 triangles. Carefully transfer the triangles to your baking sheet.
Brush each triangle with egg wash, and sprinkle with sugar. Bake for 18-20 minutes. To test doneness, scones should depress slightly when pressed. They should not be hard as a rock! Remove from oven, and let cool on the baking sheet for 5 minutes. Then, transfer to a cooling rack. Place the rack on top of the baking sheet in preparation for glazing.
When mostly cooled, glaze or frost the tops and serve. If not serving right away, glaze or frost after they're totally cooled. Store in an airtight container.