In a large bowl, whisk together all-purpose flour, almond flour, protein powder, sugar substitute, cinnamon, and salt until well combined.

Gradually add milk, one tablespoon at a time, mixing until a firm dough forms. (Whey protein may need 5 tbsp; a whey/casein blend may need 6 tbsp.)

Refrigerate the dough for 30-60 minutes to make it easier to roll.

Heat oven to 350°F (175°C). Divide the dough into two portions and place each between two sheets of parchment paper.

Sprinkle extra flour on top and roll the dough as thin as possible. Thinner dough leads to crunchier cereal.

Lightly spray the rolled dough with cooking spray, then evenly sprinkle the cinnamon sugar topping. Press gently to help it stick.

Use a pizza cutter to slice the dough into small cereal-sized squares. There's no need to separate them before baking.

Place the parchment paper with the sliced dough on a baking sheet and bake for 16-18 minutes (16 minutes for whey protein, 18 minutes for a blend).

Let the cereal cool for 30 minutes—it will harden as it cools. If it’s not crunchy enough, allow it to sit for another hour.

Once completely cooled, break apart the squares and store them in an airtight container for up to two weeks. Serve with milk, yogurt, or as a crunchy snack!