Large saucepan(All Clad stainless steel cookware is so great)
Instructions
Preheat oven to 425°F. Grease a square 8x8 baking dish with butter or cooking spray. Set aside.
Slice the zucchinis into 1/4 inch thick pieces, and place in a large bowl. Sprinkle 1 teaspoon of salt over the slices and toss gently with your hands. Set aside 20 minutes.
TIP: This step is important as it will extract the water from the zucchini to prevent a soggy, overly wet casserole. DO NOT SKIP!
Drain the zucchini slices by laying them on a kitchen towel or paper towel, patting them to remove as much excess water as you can (on both sides).
In a large saucepan, melt 2 Tbsp butter over medium heat and saute the onions until soft. Stir in garlic, heavy cream, sour cream, and 1/2 tsp salt and keep sauting until the mixture is hot and bubbly.
In a medium bowl, add all of the cheeses and mix together.
Sprinkle ⅔ of the grated cheeses into the onion mixture and stir until melted into a cheesy sauce.
Layer the zucchini slices in rows in the square baking dish. You will have about 4-6 rows of squash (depending on the size).
Pour the cheese and onion sauce over the top of the zucchini and spread evenly. Sprinkle the rest of the cheese over the zucchini.
Bake for 20 minutes; the sauce will be bubbly. Don't overbake; take a fork and make sure the zucchini is still slightly firm and remove from the oven. Sprinkle with fresh cracked black pepper and fresh chopped basil and serve!
TIP: If you don't have whipped cream on hand, you can use 1 cup of sour cream.