Place a rack in the center of the oven and preheat to 375 degrees. Grease a 9" pie dish with 1 Tbsp of unsalted butter and set aside.
Add the sugar, eggs, half-and-half or whipping cream, vanilla, liqueur, lemon zest and salt to a blender and pulse several times to blend the ingredients completely. Add the flour and blend on low speed for 1 full minute to form a silky-smooth batter.
Pour the batter into the prepared dish then scatter the blueberries evenly across the top of the batter. Place the dish or skillet onto a rimmed baking sheet (just in case it flows over) and bake for 35-40 minutes. The edges will be golden-brown and the center will be firm to the touch or just very slightly wobbly.
Remove from the oven and allow to cool slightly before dusting with powdered sugar and serving.
Notes
You can use any berry your heart desires to fill this recipe. Try strawberries or blackberries!