Cut spaghetti squash in half lengthwise and scoop out seeds and membrane. Season with salt and bake about 1 hour, or longer if needed on a baking sheet, cut side up. If you prefer the microwave, cut squash in half lengthwise, scoop out seeds and fibers and place on a microwave safe dish and cover. Microwave 8-9 minutes or until soft.
Meanwhile, in a large deep sauté pan, melt butter and add oil. Add onions, celery and carrots and sauté on medium-low for about 3 to 4 minutes, until soft.
Add the beef and season with salt. Brown the meat and cook, breaking it into smaller pieces with your spoon until cooked through.
When cooked, add the tomatoes and adjust salt and pepper to taste. Add wine and simmer until it reduces a bit, then add bay leaf and cover, reducing heat to low. Simmer at least 1 hour, stirring occasionally.
When spaghetti squash is cooked, let it cool for about 10 minutes. When cool, use a fork to remove flesh, which will come out in spaghetti looking strands.
Keep covered and set aside keeping warm until sauce is ready. Serve topped with meat sauce and grated parmesan cheese, if desired.