• 3 tablespoons unsalted butter
• 2 medium yellow onions, halved and sliced paper thin
• 8 oz thinly sliced mushrooms
What you do:
• Melt the butter in a large frying pan over medium-low heat until foaming.
• Add the onions, and let them cook, stirring rarely, until they are deep golden brown and caramelized, about 40 minutes.
• Add the mushrooms and continue cooking for the next 5 minutes.