Knead a dough from the first 5 ingredients, adding the liquid ingredients to the solid ones so that nothing clumps. Peel the onions and cut into small pieces, also cut the sausages into small pieces and sauté briefly with the onions. Drain the Brussels sprouts and halve the florets, cut the garlic into slices.
Mix the eggs, cream and mustard and season with the spices. Then grease a springform pan with margarine. Roll out the dough and place in the mold. Pull up the edge a little.
Spread the Brussels sprouts on the floor, add the onions and sausage and top up with the egg cream.
Preheat the oven to 200 ° C (convection) and bake the tart for about 30 - 40 minutes.