1. Whisk the flour, sugar, baking powder, and salt together in a medium-size bowl.
2. Add the ricotta, butter, egg yolk, milk, and vanilla, and mix with a wooden spoon until the dough comes together; or pulse in food processor until the dough forms a ball (if batter is too dry, add about 1/8 cup of water). Shape the dough into a disk with your hands.
3. Wrap dough in plastic wrap and refrigerate for at least 1 hour (can be made up to three days ahead).
4. Preheat the oven to 350º; generously grease a large baking sheet with nonstick cooking spray or oil.
5. Lightly flour a sheet of waxed paper, place the pizza dough on it, then lightly flour the top of the dough and top with another sheet of waxed paper. Using a rolling pin, roll out the dough until it's about 10 inches in diameter. Remove the top sheet of waxed paper, transfer crust, paper side up, to the baking sheet and remove remaining waxed paper. Fold in at the edge to make a 1/2-inch rim.
6. Bake the pie: Place pizza crust in oven and bake for 15 minutes.
Remove from oven and top evenly with 2 pints of the blueberries; sprinkle evenly with the sugar. Bake for another 45 minutes, top with remaining blueberries, and bake 10 minutes longer.
Remove the dessert pizza from oven and let cool on a rack for least 5 minutes.
How kids can help: Mix ingredients for the sweet dough and help roll it out. Older kids can top dough with blueberries and sugar.