Cut off 12 thin slices of bread and cut out 12 circles (approx. 6 cm Ø) with a cookie cutter. Spread oil on both sides and press into the hollows of a muffin tin (12 hollows). Bake in a preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: see manufacturer) for approx. 12 minutes until the bread is crispy and golden brown. Leave to cool down
Wash the chives, shake dry and cut into fine rolls. Remove the skin from the mackerel fillets. Cut the fillets into small pieces, removing any bones. Mix quark, 4 tablespoons crème fraîche and 2 tablespoons chives with the mackerel. Season to taste with lemon juice, salt and pepper. Fill into the bread baskets
Peel the beetroot, dice finely and mix with the remaining crème fraîche, chives and mustard. Spread on the fish cream