1Add olive oil to a large pan over medium heat, along with the butter. Let melt, then add onions. Add salt and pepper. Cook for 30-40 minutes, starting on medium heat then turning to low. Stir often.
2Once almost fully caramelized and golden brown, add balsamic glaze and stir.
3While onions are cooking, boil water and cook spaghetti until al dente. Reserve some water.
4Add Boursin cheese and thyme to onions, let melt and stir to combine with onions. Add pasta water and cheese, stir to coat pasta. Salt to taste, and serve.