Cook pasta according to package directions until al dente, then drain and return to pot.

Add butter and milk to the hot pasta and stir over medium-low heat until butter melts.

Add cream cheese cubes and stir until completely melted and mixture is smooth.

Remove pot from heat and add shredded cheddar cheese one cup at a time, stirring until fully melted.

Season with salt, pepper, and onion powder, stirring to combine.

Serve immediately while hot and creamy.