Melt 2 tablespoons butter and 1 tablespoon extra virgin olive oil in a heavy-bottomed pot over low heat. Once melted, add the sliced red onions and sliced garlic. Cook, stirring occasionally, for 30 minutes until the onions are caramelized and jammy. Do not overcook them. Season with a pinch of sugar (optional), salt, pepper, and a big pinch of crushed red pepper. Transfer the onions to a bowl and leave the pot on low heat.