Zucchini and Summer Squash Casserole

1/2 Tbsp butter
1 Tbsp olive oil
salt
pepper
1/2 cup onion, chopped
5-6 cloves garlic, minced
3 summer squash, sliced into thin rounds
3 zucchini, sliced into thin rounds
1/2 teaspoon dry thyme
1 large egg
1/4 cup heavy cream
1 1/4 cups crushed butter crackers
3/4-1 cup grated parmesan

Preheat oven to 350.
Grease a 9 x 13" baking pan with Pam or butter.
Heat the olive oil and butter in a large pot over medium-high heat.
Add the onions.
Season with salt and pepper.
Cook until soft, about 5 minutes.
Add garlic and cook about 1 minute.
Add the squash and zucchini, season with salt and pepper, and cook until tender, about 20 minutes, stirring occasionally.
Stir in the thyme and remove from heat.
Using a slotted spoon, transfer vegetables to the baking dish, reserving the cooking liquid.
Combine the egg and cream in a medium bowl. Gradually whisk in cooking liquid.
Pour over vegetables.
Bake until sets, about 30 minutes.
Sprinkle with crackers and parmesan, then bake til golden brown, 10-15 minutes.