01 -
Preheat the oven to 375°F. Blanch pearl onions in boiling salted water for 1–2 minutes until skins loosen. Transfer onions to an ice bath to cool, then peel and trim the ends.
02 -
Place peeled onions in a saucepan with water, a few black peppercorns, and bay leaves. Simmer until just tender, about 5–8 minutes. Drain and pat the onions dry.
03 -
In a medium saucepan over low heat, melt the butter. Whisk in flour and cook until lightly golden and bubbling. Gradually add milk, whisking constantly until thickened, about 5 minutes. Incorporate sage and thyme, then season with kosher salt and black pepper.
04 -
Evenly coat the onions with béchamel sauce in a baking dish. Bake at 375°F for 20 minutes, until the mixture is bubbling and the top is lightly browned.