Step 1

Bring a large pot of heavily salted water to a boil over medium-high heat. Meanwhile, finely grate 4 ounces Parmesan cheese on the small holes of a box grater if needed (about 2 loosely packed cups), or measure out 1 cup store-bought grated. Juice 2 medium lemons until you have 1/4 cup juice. Place the Parmesan, lemon juice, 1/4 cup Dijon mustard, and 1 teaspoon coarsely ground black pepper in a medium bowl and stir to combine. Finely chop 8 garlic cloves (3 to 4 tablespoons).

Step 2

Add 1 pound dried spaghetti to the boiling water and cook for 2 fewer minutes than indicated in the package directions; the desired outcome is al dente. Meanwhile, melt 1 tablespoon of the unsalted butter in a small frying pan over medium heat. Add 1/4 cup panko breadcrumbs and cook, stirring often, until toasted and golden brown, about 2 minutes. Remove the pan from the heat. Drain 2 (2-ounce) tins anchovy fillets (1/3 cup).

Step 3

Reserve 2 cups of the pasta cooking water, then drain the pasta. Wipe out the pot, add the remaining 2 tablespoons unsalted butter and 2 tablespoons olive oil, and place over medium heat until the butter is melted. Add the anchovies and cook, stirring constantly, until they start to dissolve and look like a loose paste, 2 to 3 minutes. Add the garlic and cook until fragrant, about 1 minute. Add 1 teaspoon red pepper flakes if using and cook for 30 seconds.

Step 4

Increase the heat to medium high and add 1 1/2 cups of the reserved pasta water. Add the Dijon mixture and whisk until the sauce is smooth and begins to thicken slightly, 2 to 3 minutes. Add the spaghetti and cook, tossing to coat in the sauce and adding some of the remaining pasta water as needed, until the sauce thickens and clings to the pasta, about 1 minute. Turn off the heat. Taste and season with salt as needed.

Step 5

Divide the pasta among bowls and garnish with the toasted breadcrumbs, more grated Parmesan cheese, and more coarsely ground black pepper.