Buckwheat mushroom tartlets

Name: Buckwheat mushroom tartlets
Prep time: 20 min
Cook time: 1 h 45 min
Total time: 1 h 45 min
Yield: 24 pieces
Ingredients: 200 g buckwheat groats; ¼ tsp salt; 100 g unsalted butter; 50 g water; 1 egg; gluten free flour mix; 40 g Parmesan cheese; 300 g fresh Swiss brown mushrooms; 1 brown onion; 1 sprig fresh flat-leaf parsley; 20 g unsalted butter; 20 g vegetable oil; 1 tbsp gluten free flour mix; 100 g full cream milk; 1 egg; 50 g thickened cream; 1 tsp salt; ¼ tsp ground black pepper; 1 pinch grated nutmeg; 10 sprigs fresh chives