Preheat the oven to 160 ° C (convection). Line the hollows of a muffin tin with the paper liners.
Mix the oat flakes with the buttermilk in a small bowl. In another bowl, mix the two types of flour with the cinnamon, baking powder and baking soda.
In another bowl, whisk the egg lightly, add sugar, applesauce, oil and the oatmeal buttermilk mixture and stir. Add the flour mixture and stir only until the dry ingredients are moist.
Pour half of the dough into the molds, place a piece of chocolate on top and cover with the rest of the dough. Then sprinkle with a little brown sugar and bake for 20-25 minutes.
Take out of the oven and let rest in the tray for about 5 minutes. Then let cool on a wire rack.