Boil the milk, thyme, nutmeg, cloves, bay leaf and garlic for 1 minute, stirring constantly, then remove from heat and cool. Strain the mixture, reserving the fluids.
Bring the milk mixture to a boil, whisk in the flour, then reduce the heat and simmer until thick, whisking constantly. Add the wine and butter and cook until the butter melts, then remove from heat and add the Gruyere, stirring until the cheese melts. Season to taste.
Arrange the leeks in a buttered baking dish, pour the mixture over the leeks, sprinkle with the Parmesan and red pepper, then bake at 400 until lightly browned.