Bring a large covered pot of salted water to boil over high heat. Heat oven to 450 degrees Fahrenheit.
Arrange asparagus in one layer on a metal sheet pan. Drizzle with olive oil and season with salt and pepper. Set aside.
To a medium-sized saucepan, add butter and melt over medium heat. Slowly add flour to the melted butter, whisking to incorporate. While continuing to whisk, stream in the milk and allow to come to a boil. Simmer over medium heat until thickened. Add sour cream, dry mustard and cheeses and stir until cheese is melted. Season with salt and pepper and set aside.
Cook asparagus in oven for 8-10 minutes, shaking the pan halfway through. Turn on the broiler to high heat and broil for an additional 2-4 minutes, watching closely to prevent burning.
While asparagus is cooking, add orecchiette to boiling water and cook until al dente. Strain pasta and return to pot. Add cheese sauce and stir to combine. Serve topped with charred asparagus.