Combine melted butter and flour, and cook over medium heat to form a roux. Set aside.
In a medium saucepan, bring the milk, shallot, bay leaf, and cloves to a simmer. Remove from heat and let steep for 30 minutes. Discard the shallot, bay leaf, and cloves.
Bring milk back to a simmer and whisk in the roux until smooth. Cook over low heat, stirring continuously, for 10 to 15 minutes. Season with salt, white pepper, and nutmeg.
Remove from heat, then stir in the cheeses and herbs. Let cool to room temperature.
Top each oyster with 1 tablespoon of sauce and bake in a preheated oven set at 400℉. Top with toasted breadcrumbs and serve.