Cook pasta shells according to pasta instructions for "al dente". Drain and set aside.

In a saucepan over medium heat, add butter and begin to melt. Add flour and stir to form a paste. Slowly Add milk to the flour mixture while stirring. Add salt, pepper, and garlic powder and stir. Bring sauce to a simmer. Reduce heat to low and stir in white cheddar cheese. Stir until cheese is fully melted into the sauce.

Toss pasta shells in with the cheese sauce and serve immediately.