Place 1/2 cup salted butter in a large saucepan and heat on high for about 5 minutes. Whisk often while heating. The butter will start to sizzle and froth up. Watch for brown flecks (not black) and remove from heat. Set aside to cool to room temperature. Stir well once the butter is cool, it will be a thick paste.

Place 3 tablespoons butter into a large skillet. Add the onions and cook over high heat while stirring often. Once the pan is very hot, move the onions aside and slowly drizzle in a tablespoon or 2 of the beef broth. This will deglaze the pan and caramelize the onions. Continue with the rest of the broth 3 more times throughout the cooking. Remove the onions from the skillet once they are brown and caramelized and set aside. Leave the drippings in the skillet.

Place the mushrooms and garlic into the skillet (add more butter if needed). Cook the mushrooms over high heat while stirring often until the mushrooms are browned. Season lightly with salt. Remove from heat and set aside.

Once the onions and mushrooms are at room temperature (not too hot or they will melt the brown butter on the board, start to assemble your butter board.

Use a knife to smear the brown butter paste onto a clean wooden board. Top the brown butter with the onions, then the mushrooms and garnish with fresh herbs if desired.

Serve with slices of protein sparing bread and if you are like me, serve the butter board with a tenderloin steak!