Directions:

• Preheat the oven to 450 degrees F.
• Bring a large pot of salted water to a boil and cook the spaghetti according to package directions for al dente. Drain and set aside.
• Melt 2 tablespoons of the butter in a large heavy-bottom pot or Dutch oven over medium-high heat. Add the mushrooms, 1/2 teaspoon salt and a few grinds black pepper and cook, stirring occasionally, until the mushrooms have softened and released their liquid, 5 to 6 minutes. Add the shallots, minced garlic and red pepper flakes and cook, stirring occasionally, until the shallots soften, 3 to 4 minutes.
• Add the wine and bring to a boil, stirring to combine. Cook, stirring frequently, until reduced completely, 5 to 6 minutes. Stir in 2 tablespoons of the butter until melted, then sprinkle in the flour and stir until well combined with the vegetables. Slowly pour in the cream, then add the lemon juice, 1 teaspoon salt and a few grinds black pepper. Simmer, stirring occasionally, until the sauce is slightly thickened and no longer has a floury taste, 6 to 8 minutes. Add the pasta and cheese and toss until pasta is well coated. Transfer to a 3-quart casserole dish.
• Meanwhile, microwave the remaining 4 tablespoons butter in a small bowl until melted, about 1 minute. Stir 2 tablespoons of the melted butter and 1/2 teaspoon salt into the panko in a small bowl; set aside. Toss the remaining 2 tablespoons melted butter with the shrimp, grated garlic, 1/2 teaspoon salt and a few grinds black pepper in a medium bowl. Scatter the shrimp evenly over top of the pasta, then sprinkle with the panko mixture.
• Bake until the shrimp are opaque throughout and the topping is slightly golden, about 10 minutes. Let sit for 10 minutes before sprinkling with the parsley.