How to Make It
Combine flour and butter in a bowl until a paste forms.
Place a large high-sided sauté pan over medium-high heat. Add oil to pan; swirl to coat. Add pancetta; cook 2 minutes, stirring frequently. Add mushrooms; sauté 5 minutes or until browned and liquid evaporates. Add wine; cook 2 minutes or until liquid is absorbed, stirring to loosen browned bits. Stir in 1/4 teaspoon salt. Transfer mixture to a plate.
Add stock, 2 cups milk, penne, and bay leaf to pan; bring to a boil. Cook 8 minutes, stirring occasionally. Stir in peas, asparagus, and 1/2 teaspoon salt; cook 2 minutes, stirring frequently. Stir in remaining 1/4 teaspoon salt, remaining 1 cup milk, and thyme; cook 2 minutes. Add butter-flour paste, in pieces, stirring constantly to combine and thicken. Remove from heat; stir in mushroom mixture, parsley, rind, and black pepper.