Caramelized onions and mushrooms that's sweet from the caramelized onions, earthy mushrooms, and dotted with pieces of fresh thyme.
Melt the unsalted butter in a large, heavy bottomed frying pan over medium heat. Drizzle the olive oil and let it warm for 30 seconds, swirling with the melted butter.
Add the sliced yellow and red onions to the pan. Toss the onions to coat them in the melted butter and oil. Let the onions cook at medium heat, stirring occasionally. Continue to cook the onions until they reduce and become translucent, about 5 minutes.
Turn the heat under the pan down to medium-low. Pour the sea salt and the sugar over the onions. Toss to incorporate and cook additional 7-8 minutes. The onions will develop a deep brown color.
Carefully pour the sherry into the pan and stir to incorporate. Add the sliced baby portobello mushrooms and fresh thyme into the pan and stir to incorporate into the onions. Cook the mushrooms until they are tender and evenly browned, about 10 minutes.
Remove the pan from the heat, taste, and season with flaky salt and pepper to taste. Enjoy!