Preheat oven to 400 F. Halve and core acorn squashes. Rub with olive oil and sprinkle with salt and pepper. Bake for 10-15 minutes. (will return back to oven).
Melt butter in a medium saucepan over medium heat. Add garlic and cook for 30 seconds or until fragrant. Whisk in flour to butter mixture and cook until smooth and golden in color, about 1-2 minutes.
Slowly add in the milk and heavy cream, whisking as you pour. To the cream, add in salt, pepper, and rosemary to cream mixture. Cook for 3-4 minutes, the mixture should be thick enough to coat the back of a wooden spoon. Remove cream mixture from heat and whisk in shredded white cheddar cheese and 1 cup of shredded gruyere until smooth.
Prepare cauliflower pears in the microwave according to package instructions. Add pearls to the cheese sauce.
Fill acorn squashes with cheesy cauliflower and top with remaining gruyere cheese. Bake for 25- 30 minutes or until squash its tender and top is golden brown.
Optional: Bake cauliflower in a greased casserole dish instead of acorn squashes.