Preheat oven to 350 deg Fahrenheit
In a large pan, over medium heat, saute leeks and butter, stirring frequently until leeks are soft with a gold tint to them
Add celery and asparagus, stir every minute or two for about 6 minutes to ensure vegetables cook evenly
Add garlic (adding it after the vegetables ensures it won’t brown or be bitter)
Add cream, give one quick stir, and let the cream bubble lightly for about two minutes before transferring to a casserole dish
Delicately toss the cheese evenly across the gratin, make sure not to stir it in.
Bake for 30-40 minutes until cheese is melted or golden brown