Peel the onions and slice into fine rings. Wash the thyme, dab dry and pluck off the leaves, except for a little to garnish. Heat the fat in a pan and fry the onions in it until golden brown.
Finally add thyme and season with a little salt and pepper. Cut the cheese into small slices. Place slices of bread on a baking tray lined with baking paper. Spread onions on the bread slices and cover with the two cheeses.
Bake in the preheated oven (electric cooker: 225 °C/ convection oven: 200 °C/ gas: level 4) for approx. 5 minutes. Arrange slices of bread on a plate and sprinkle with remaining thyme. Serve garnished with cherry tomatoes.