Measure out 4 cups of spaghetti squash strands, draining off any excess liquid, and set aside.
Heat olive oil in a small skillet over medium heat. Add diced onion and saute for about 5 minutes or until tender.
Add cooked onion, strands of spaghetti squash, sour cream, ½ cup of cheddar cheese, whisked eggs, garlic powder, and salt to a large bowl and mix to combine.
Spread the mixture into an 8 x 10 casserole dish or regular-sized muffin pans sprayed with non-stick cooking spray (will make 18 au gratin cups.)
Sprinkle remaining cheddar cheese over the top of the spaghetti squash mixture.
Bake for about 25 minutes or until firm and starting to brown on top.
Turn oven to broil and cook for 2-3 minutes more to crisp the tops.
Allow spaghetti squash au gratin to cool for 10 minutes before serving.
Video
Notes
Check out process pictures and more details above!Expert tips and notes:
Use Greek Yogurt instead of sour cream for more protein.
To cook spaghetti whole:
Stab the outside gourd with a sharp knife to allow steam to escape while cooking. Insert knife tip about ½ an inch. Make at least 10 cuts or more for larger gourds.
Place spaghetti squash in a slow cooker and cover or place in the oven preheated to 425°F on a baking sheet.
Slow cooker: Cook on low for 5-6 hours or high for 3-4 hours or until a knife can be easily inserted into the gourd.
Oven: Roast for about 30 minutes, rolling over halfway through.
Allow the spaghetti squash to cool for about 10 minutes. Cut in half and remove seeds. Scrape the spaghetti squash strands from the insides of the squash halves with a fork.
To cut in half and then cook:
Cut the spaghetti squash in half and scoop out the seeds.
Brush the inside with olive oil and season with salt and pepper.
Place squash halves, flesh side down, on a sheet pan lined with aluminum foil.
Bake for 40 minutes in a 375°F oven or until the flesh is tender to touch.
There are several options to make the recipe ahead of time:
Cook the spaghetti squash ahead of time and refrigerate the spaghetti strands until you are ready to make the recipe (up to 5 days.)
Prepare the recipe the day before and cook it the next day.
Prepare and cook the recipe and reheat it the next day.
Freezer options:
To freeze this recipe uncooked, add everything to a freezer-safe dish, cover tightly, and freeze for up to 2 months. Defrost overnight in the refrigerator and cook as usual.
If already cooked when frozen, reheat the casserole in a 350°F oven so that the internal temperature reaches 145°F. We do not recommend using the microwave.
For either option, tent with foil if browning too quickly.