Preheat a medium skillet over medium heat.
In a small mixing bowl, whisk together the flour, protein powder, baking powder, and salt. Set aside.
In a medium mixing bowl, use a fork to mash the banana until almost smooth.
Stir in the remaining wet ingredients (honey, sourdough starter, milk, eggs, melted butter, and vanilla extract) with a rubber spatula or spoon.
Slowly stir the dry ingredients into the bowl of wet ingredients and mix until just combined. The batter should still be somewhat lumpy.
Melt a small amount of butter of butter in the now preheated pan. Use a ⅓ cup measuring cup to scoop the batter into the pan.
Allow the pancakes to cook approximately 2 minutes. The pancake should appear cooked along the edges and bubble in the center. Flip and cook another 1-2 minutes on the other side.
Cook the remaining batter and serve warm.