For the sauce, heat the butter and add the flour while stirring. Stir in milk and broth in portions. Let the sauce simmer over low heat. Season with pepper.

Cut the onions and garlic into small cubes and fry until translucent. Cut the beetroot into cubes and fry briefly with the onions and garlic. Dice the apple and mix in the crumbled feta, season with fresh thyme.

First, pour the sauce into the baking dish so that the bottom is covered. Then add a layer of lasagne sheets and the filling on top, another layer of sauce and then lasagne sheets on top. Continue in this order and finish with a layer of lasagne sheets, then add more sauce and finally spread the grated Gouda.

Bake in the oven for about 50 minutes.