Preheat oven to 400F
Slice acorn squashes in half carefully. Cover the inside of all four halves with about 1/2 tbsp olive oil each (for a total of 2 tbsp). Season with salt and pepper to taste. Place cut side down on a foil-lined baking tray and bake until soft and a bit golden, about 30-45 minutes
While squash is baking, make the stuffing. First, cook the rice - boil 1 cup water, add rinsed rice and some salt to taste, cover and reduce heat to low and cook for about 12-14 minutes until water is fully absorbed
In a large skillet over medium-high heat, add 2 tbsp olive oil. Once hot, add sage leaves and fry for a minute, then add beef. Break up with a wooden spoon and cook until browned, seasoning with salt and pepper. Add shallots, garlic, and thyme, cooking until shallots are soft
Stir in rice and heavy cream, then add 1/2 cup of cheese. Stir to combine and let simmer for a few minutes
Get the acorn squash out of the oven and flip over. Stuff each of the four halves with 1/4 of the stuffing (or as much as will fit), then top with remaining cheese. Bake for 10 minutes, until cheese is melty and browned