Step 1

Arrange a rack in the upper third of the oven and heat the oven to 425°F.

Step 2

Trim the ends from 1 pound asparagus and place on a rimmed baking sheet. Drizzle with 1 teaspoon olive oil and toss to coat. Arrange so the spears are in a single layer side-by-side and touching.

Step 3

Grate 1 ounce Parmesan cheese on the small holes of a box grater into fine shreds (about 1/2 cup), or measure 1/4 cup store-bought grated. Grate 1 garlic clove on the same holes of the box grater, or mince.

Step 4

Melt 1 tablespoon unsalted butter in a small skillet over medium heat. Add the garlic and cook until fragrant, 30 seconds to 1 minute. Sprinkle in 1 tablespoon all-purpose flour and whisk for 30 seconds to 1 minute to cook the floury taste out. While whisking constantly, slowly pour in 1 cup whole or 2% milk. Continue whisking occasionally until smooth and simmering. Cook, stirring constantly, until the sauce is slightly reduced and thickened enough to coat the back of a spoon, 2 to 3 minutes.

Step 5

Remove the pan from the heat. Add 1/4 teaspoon kosher salt and two-thirds of the Parmesan, and stir until melted and smooth.

Step 6

Pour the Alfredo sauce across the center of the asparagus, covering most of it. Sprinkle evenly with the remaining Parmesan.

Step 7

Roast until the asparagus is crisp-tender, 10 to 12 minutes. Turn on the broiler to high and broil until the top is golden-brown in spots, 1 to 3 minutes. Top with a few grinds of freshly ground black pepper before serving.