Pre-heat oven to 425 degrees. Put butter in 9x13 pan and set in oven to melt. While butter is melting, put eggs in blender and blend on high for 1 minute. Gradually add milk, then flour slowly. Blend for 30 seconds. Remove 9x13 from oven. Pour the batter into the hot melted butter. Return to oven and bake until puffy - 20 minutes.
Serve immediately with lemon wedges and powdered sugar.