Butter both slices of bread.

Place one slice butter side down in cast iron grill pan, then top with sliced sharp white cheddar.

Add leftover roasted garlic & onions, then top with some shredded cheddar-Jack.

Top with second slice of bread, butter side up.

Cook the first side over medium heat until browned, then flip and cook the other side until browned.

Remove sandwich from pan and add avocado slices.

Enjoy!