Cut ice cold butter into cubes ( I swear by Kerrygold for scone baking)
Blend together with a pastry cutter until it looks like little peas are forming. Don't overwork the dough. Freeze for 10 minutes
Preheat oven to 450°
Take bowl out of freezer and add most of (about 3/4 cup) of the heavy cream. Mix gently.
Fold in the blueberries and 1 tsp of the lemon zest
Make a cross out of wax paper and cover the bowl. Gently tip over the bowl with the wax paper on the top. Fold the sides up and mix the dough with your hands for about 30 seconds. Be very gentle.
Spoon the dough into a scone pan and gently pat into the corners. Drizzle the remaining cream on top.