Toss the raw lingonberries with sugar and leave them to stand for at least 1 hour. This can also be done the day before and kept in the fridge.
Heat the butter in a saucepan and sauté the finely chopped shallots and garlic. Add the flour and cook thoroughly. Pour in the wine and bring to the boil, whisking continuously. Then pour in the stock, add the bay leaf and simmer for 10 minutes. Add the cream and bring to the boil. Add the grated cheese and season to taste with lemon juice, salt and pepper.
Boil the potatoes in salted water until tender, peel them and cut them into bite-sized pieces. Cut off the top third of the leeks (the dark green part) and clean them thoroughly. Slice them into 2 cm pieces and place them in a saucepan with 3 tbsp water, 1 tbsp butter and a little salt. Steam them under a lid until tender for approx. 8–10 minutes.
Warm the tartlets in the oven.
Pour the leeks into a sieve, then toss them together with the potatoes in the cheese sauce. Divide the leek and potato mixture between the warm tartlets, sprinkle with a few lingonberries, top with cress, and finally grate a little cheese over the top. Serve immediately.
