Preheat the oven to 400 degrees Fahrenheit (204 degrees Celsius) and line a baking sheet with parchment paper.

In a large mixing bowl, whisk together the self-rising flour, unflavored protein powder, and salt until well combined.

Create a well in the center of the dry ingredients and add the Greek yogurt and liquid egg whites.

Using a spatula, gently fold the wet ingredients into the dry ingredients until a shaggy dough forms, taking care not to overwork the gluten.

Turn the dough onto a lightly floured surface and pat it down to a 1-inch thickness. Fold the dough over itself three times to create layers.

Use a 3-inch biscuit cutter to stamp out 6 biscuits, pressing straight down without twisting.

Place the biscuits on the prepared baking sheet so they are just touching to encourage a higher rise.

Bake for 12 to 15 minutes, or until the tops are golden brown.

Remove from the oven and immediately brush the tops with melted butter before serving.