Heat 1 tbsp of olive oil in a pan over medium heat. Add onions and cook, stirring often, until they've shrunk to half their size and have a dark caramel color. Remove from pan. 

Heat 1 tbsp of olive oil in the pan to a medium heat and cook until they have a golden sear and there is no liquid left. Meanwhile, cook pasta according to package directions. 

In the empty pasta pot, heat 1 tbsp olive oil over a low heat and add sage and garlic, cooking until fragrant. Add pasta, mushrooms, onions, and cheese. Stir until combined and season with salt and pepper.