Preheat the oven to 180C convection.
Rub the quince well with a cloth.
Place the quinces with their peel on a baking sheet and cook for about 40 minutes, until the fruits are soft.
Take the quinces out of the oven and cover with a damp kitchen towel.
While the quinces are cooling slightly, toast the bread in the middle of the oven for about 5 minutes.
Slice the cheese and place on the bread slices. Leave the cheese slices in the oven for another 3 minutes so that the cheese melts easily.
Halve the quince, remove the core and extract the pulp from the skin. Then lightly press the pulp with a fork.
Distribute the pulp evenly on the cheese slices, distribute the thyme leaves on the tartines and season with salt flakes and pepper.