Preheat BBQ to 350°F
In a medium saucepan, melt butter.
Add flour, salt, pepper and garlic powder, stirring until thickened.
Slowly add cream, 1 cup at a time alternating with the cream cheese, (¼ of the cream cheese at a time), Whisking between additions and allowing the cream cheese to melt before the next addition
Add medium cheddar and old cheddar, about ½ cup at a time, stirring. Allow cheese to melt before adding the next addition.
Fold in Parmesan and jalapenos
Place cooked macaroni in a deep 13" by 9" pan
Pour cheese sauce over macaroni and carefully stir
Top with shredded old cheddar
Place on preheated BBQ over indirect heat
Allow to heat through until cheese on top is fully melted about 30 minutes
Serve hot.
