In a large pot, melt some butter and cook the shallot and garlic.
Add the mussels to the pot, then the white wine.
Cover and cook for 10 minutes, stirring the mussels occasionally.

Shell the mussels and set them aside. Filter the mussel juice and reserve 2 cups (500 ml).

In a saucepan, melt the butter and add the chopped leek.
Cook for 10 minutes over low heat, stirring regularly.
Sprinkle the flour over the mixture and stir well.
Add the reserved mussel juice and stir until thickened.
Add the cream and pepper, then the mussels and stir gently.

Divide the mixture among 6 mini-cocottes or small gratin dishes and top with grated smoked gouda cheese.
Put under the grill until the cheese is melted and golden brown.
Serve immediately.