Preheat the oven to 200 degrees F (for keeping the pancakes warm). Grate 3/4 teaspoon lemon zest and then squeeze 1 tablespoon of juice; reserve separately. Put one bag of the blueberries, the maple syrup, lemon juice and 1/4 teaspoon of the lemon zest into a small (8-inch) skillet with 1/3 cup water. Bring to a simmer over medium heat, stirring occasionally, and continue to simmer until the mixture is syrupy and thickened, 6 to 8 minutes. Remove the blueberry sauce from the heat and set aside. (You should have about 3/4 cup.)
Meanwhile, whisk the cake mix, sour cream, eggs, the remaining 1/2 teaspoon lemon zest and 1 cup water in a large bowl until smooth and thick.
Heat a large nonstick skillet over medium heat; lightly coat with cooking spray. Drop the batter by 1/4-cupfuls into the skillet, leaving 1 inch between each. Cook until bubbles rise to the top of the pancakes and they are set around the edges and lightly browned on the bottom, 5 to 7 minutes. Add about 5 blueberries to the top of each pancake and then carefully flip (the tops of the pancakes will still be a little soft). Continue to cook until lightly browned and cooked through, 5 minutes more. Transfer to a baking sheet and keep warm in the oven. Repeat with the remaining batter.
Top the pancakes with the blueberry sauce and a dusting of confectioners' sugar. Serve with butter and maple syrup on the side.
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