Preheat oven to 350°F.
Blend 2 cups half and half, chipotle pepper(s), bouillon cubes and garlic in blender or food processor until well blended.
Pour into a large saucepan and add onion powder, black pepper, remaining 2 cups of half and half and corn starch. Stirring constantly, bring to a boil. Continue to stir and boil for 1 minute or until very thick. Remove from heat.
Gradually stir in cheeses until melted. Add cooked pasta and stir until blended. Pour mixture into a greased 3-quart casserole dish (or 13 x 9-inch pan) and sprinkle with topping.
Bake for 25 to 30 minutes or until browned and bubbly around edges.