In a large bowl add the buckwheat and all-purpose flours, sugar, baking soda, and salt. Whisk to combine. In a medium bowl add the milk, egg, and butter and whisk to combine. Add the wet ingredients to the dry ingredients and whisk to combine.
Heat a large skillet over medium-high heat and spray with cooking spray. Add 1/2 cup of the pancake mixture and cook until bubbly and dry around the edges, flip and cook for 30-60 seconds more. Repeat with remaining batter.
Top each serving with some banana slices and serve with your syrup topping of choice.