Preparation:

1 Preheat the oven to 200°C (thermostat 6/7).

2 Peel the leeks, cut them into quarters lengthwise and slice them roughly.
Place them in a colander and rinse them thoroughly to remove soil and impurities.

3 Peel and finely chop 2 cloves of garlic.

4 Heat a pan over medium heat with 2 knobs of butter and a drizzle of olive oil. Add the garlic.

Take the leaves from 6 sprigs of thyme (2 for me). When the garlic is just starting to brown, add the leek and thyme. Mix well, place over high heat and cook for 10 minutes, until cooked and softened.
5 Meanwhile, grate 100 g of Cheddar (for me Parmesan). Remove the pan from the heat, season with salt and pepper (salt lightly because there is some in the cheese). Add 20 cl of liquid cream (10 for me) and half of the cheese.

Mix the mixture well and then pour it into a baking dish of adequate size to have, in the end, a thickness of vegetables of about 2.5 cm.
I used a terracotta baking dish of 23 cm in diameter.

6 Sprinkle with the remaining cheese and bake for about 20 minutes, until the surface of the dish is golden and appetizing.