In a mixing bowl, stir together the protein powder, oats, peanut butter, and maple syrup. If desired, you can add chocolate chips.
Mix with a spatula or fork until a smooth dough forms.
If the dough is too dry, add a splash of milk or a little more peanut butter. If it’s too wet, mix in extra oats or a bit more protein powder to bring it together. Casein and vegan protein powder absorb more moisture than whey.
Scoop out portions of dough and roll them into bite-sized balls with your hands. To prevent sticking, lightly dampen your palms or dust them with oat flour.
Place the protein balls on a tray or in a container and chill in the fridge for 30–60 minutes to help them firm up. Store leftovers in an airtight container in the fridge for up to 5 days.