Preheat your oven to 180°C (356°F). Line a baking sheet with parchment paper or lightly grease it.

In a mixing bowl, combine the oat flour, cottage cheese, eggs, salt, vanillin, stevia, and baking powder. Stir until well mixed. You might notice the dough is quite soft, which is normal.

Dust your work surface lightly with flour. Roll the dough out into a rectangle, about 0.5 cm thick.

In another small bowl, whip the egg white until frothy. Mix the cinnamon with the egg white and spread this mixture evenly over the rolled-out dough.

Roll the dough tightly from one long edge to the other to form a log shape. Slice the log into evenly-sized rolls, about 2.5 cm thick.

Place the rolls on the prepared baking sheet, cut side up, and bake for 30-40 minutes or until they turn golden brown.

While the rolls are in the oven, prepare the creamy filling. Heat 300 ml of milk in a pot until just hot, but not boiling.

In a separate bowl, whisk together the egg yolk, remaining egg, starch, and 2 tablespoons of stevia until smooth. Gradually stir in 100 ml of the hot milk until well combined.

Pour the egg-milk mixture into the remaining hot milk in the pot. Cook over low heat, stirring constantly, until the mixture thickens into a creamy filling.

Once the rolls are baked, let them cool slightly before serving. Drizzle the creamy filling over the top and sprinkle chopped walnuts if desired.