Blanch asparagus in salted boiling water for 1 minute.
Remove and plunge into a bowl of ice water. When asparagus is thoroughly cold, drain and set aside.
Melt 4 tablespoons of the butter in a large skillet over medium-high heat. Add onions and caramelize, stirring occasionally, until soft and deep gold in color, about 20 minutes. Add milk and bring to a boil for 1 minute to thicken slightly.
Transfer to a blender and puree until smooth. Add 1 tablespoon of the butter and puree again until incorporated. Sauce should be thick, creamy and pourable. Season with salt, pepper, lemon juice and nutmeg. Keep warm until ready to serve.
In the same pan, melt the remaining tablespoon of butter and briefly heat asparagus through. Pour some sauce in the middle of the serving platter. Arrange asparagus spears and spoon more sauce over asparagus.
Garnish with grated lemon zest, if desired.
What's Soubise Sauce?
A soubise sauce is a simple French sauce traditionally made with sautéed onions and cream. Here, we’ve made it Georgia Grown with sweet caramelized Vidalia onions and whole milk from Georgia farmers.