Whisk dry ingredients: In a large bowl, whisk together the cake mix, protein powder, and salt until no clumps remain, about 30 seconds. This keeps the protein powder from clumping once the wet ingredients go in.

Add peanut butter and honey: Add the peanut butter and honey to the dry mix. Stir with a sturdy spoon until the mixture starts to clump together, about 1 minute.

Stir in vanilla: Add the vanilla extract and continue stirring until a thick, slightly stiff dough forms, similar to cookie dough. The dough should hold together when pressed between your fingers.

Adjust with milk: If the dough feels dry or crumbly, add milk one tablespoon at a time, mixing after each addition. Stop once the dough is smooth and holds its shape without sticking heavily to your hands.

Fold in sprinkles: Add the rainbow sprinkles to the dough and fold gently with a spatula. Fold just until they're distributed, so the colors stay distinct instead of bleeding into the dough.

Fold in chocolate chips: Add the mini chocolate chips and fold them through the same way. The dough should look speckled with color and small dark chips.

Scoop the dough: Using a tablespoon or small cookie scoop, portion the dough into 16 equal pieces. Keep the portions even so the balls chill and firm up at the same rate.

Roll into balls: Roll each portion between your palms into a smooth, 1-inch ball. If the dough sticks to your hands, lightly dampen your palms with a little water.

Arrange and chill: Place the rolled balls on a parchment-lined plate or tray, spaced slightly apart. Chill in the refrigerator for 20 minutes, until firm to the touch.

Store the balls: Transfer the chilled balls to an airtight container. Keep them in the fridge for up to one week or in the freezer for up to 3 months.