1. In a large bowl or mixer, begin making your batter by combining milk, water, butter, eggs, flour, salt and sugar. Mix until the batter is smooth and there are no lumps. Refrigerate for at least 1 hour (or up to 12).
2. In a saucepan, for your filling, mix blueberries, sugar, lemon zest, lemon juice and cinnamon together, and place over medium heat. Bring mixture to a boil, then quickly reduce heat and let simmer for 2-3 minutes. Remove from heat.
3. Take an 8-inch crepe pan (important to have a small pan to insure size and thickness of blintzes) and add a small amount of butter. Place over medium heat.
4. When the pan is hot, pour in a 1/4 cup of batter and slowly tilt the pan to evenly spread the batter in a circle, until the bottom is completely covered.
5. Cook for 45-60 seconds, or until the batter is just set and the bottom is browned; flip to brown the other side. Remove to a plate and cover to keep warm. Repeat with the rest of batter.

Assembly

1. Use a slotted spoon to put 1-2 tablespoons of berry mixture (leaving sauce to drizzle over the top) on the lower third of the blintz. Fold the bottom up and over the filling, tuck in both sides (like a burrito) as you go and roll towards the top of the blintzes. You should end with the seam side down. Repeat with rest of blintzes.
2. Optional: Add some more butter to your pan and lightly fry each blintz for a golden crisp outer edge OR place in a 375º F oven until warmed through.
3. Remove to a serving platter and garnish with leftover berry sauce and powdered sugar.