Roll dough, cut to fit tart moulds and press into greased moulds. Pierce bottom several times. Melt butter in pan, then put aside.
Mix egg yolk and fresh cream in container. Season with salt and pepper.
Peel potatoes and cut into even, thin slices.
Pour mixture into moulds and top with layered potato slices. Baste with melted butter.
Bake mini quiches in oven preheated to 180 °C for around 20-25 minutes. Let cool briefly.
Skin and seed tomatoes and dice pulp. Dice Vacherin Fribourgeois AOP as well. Mix both in container and season with pepper. Place on top of warm tarts, garnish with fresh thyme leaves and serve immediately.