Preheat broiler to high (or oven to 500 degrees). Thinly slice the garlic. Trim and discard the bottom inch of the asparagus, then cut into 2-inch pieces.

Heat 1/2 tablespoon olive oil in a large oven-proof pan over medium heat. Add the asparagus and cook, tossing, for 1-2 minutes, until bright green. Add garlic and cook another 30 seconds, until fragrant. Season with salt and pepper.

Add the milk, stock concentrate, and 2 tablespoons pesto to the pan. Stir to combine, then add the tortellini. Don't worry if the tortellini aren't covered! Bring to a boil, then reduce to a simmer and cook for 5-7 minutes, until sauce becomes slightly thickened and tortellini soft. Taste and season with salt and pepper. You can add a splash of water if the sauce becomes too thick!

While tortellini simmers, combine panko, Parmesan, and 1/2 tablespoon olive oil in a small bowl. Season mixture with salt and pepper, then sprinkle panko mixture on top of the tortellini. HINT: If you don't have an oven-proof pan, transfer tortellini to a baking dish and top with the panko mixture.

Transfer pan to the oven and broil for 1-2 minutes, until browned and bubbly.

Divide gratin among bowls and dig in!