Whisk the Dry Ingredients: In a large bowl, whisk the flour, protein powder, baking powder, salt and sugar for 30 seconds until no clumps of powder remain.
Mix the Wet Ingredients: In a second bowl, whisk the yogurt, milk, eggs, vanilla and cooled melted butter until completely smooth with no streaks of egg white.
Combine and Rest: Fold the wet mixture into the dry until just combined, leaving a few small lumps. Rest the batter 5 minutes until thick but pourable, adding 1 to 2 tablespoons of milk if stiff.
Heat the Pan: Warm a nonstick skillet or griddle over medium-low heat for 2 to 3 minutes and brush lightly with butter. A drop of water should sizzle and dance.
Cook the First Side: Scoop 1/4 cup of batter per pancake and cook 2 to 3 minutes, until bubbles form on top and the edges look set.
Flip and Finish: Flip and cook 1 to 2 minutes more until golden brown and springy. Keep finished pancakes on a wire rack in a 200°F (95°C) oven while you cook the rest.