Boil a large pot of salted water and cook pasta shells according to package instructions until al dente; drain and set aside.

Pat steak cubes dry with paper towels and season thoroughly with salt and pepper.

Heat vegetable oil in a large heavy-bottomed skillet over high heat until just beginning to smoke.

Sear steak cubes in batches for 2 minutes per side until a brown crust forms; remove steak from skillet and set aside.

Reduce skillet heat to medium and add 2 tablespoons of butter and minced garlic; sauté for 60 seconds until fragrant.

Return steak to the skillet, tossing with the garlic butter and chopped parsley for 30 seconds, then remove from heat.

In a separate medium saucepan, melt the remaining 2 tablespoons of butter over medium heat; whisk in flour and cook for 1 minute to create a roux.

Gradually whisk in milk and minced chipotle peppers, simmering until the sauce thickens enough to coat the back of a spoon.

Remove the saucepan from heat and stir in the shredded white cheddar until completely melted and smooth.

Fold the cooked pasta shells into the cheese sauce and serve immediately topped with the garlic butter steak bites.