brown butter:

• Place the butter in a pan over medium heat and stir butter the entire time to keep it moving. Once its melted, the butter will begin to foam and sizzle. Keep stirring. In about 5–8 minutes, the butter will start to turn golden brown and some of the foam will subside. It will smell intensely buttery and nutty.
• Immediately remove the pan from heat and pour the browned butter into a heatproof bowl to stop the cooking.
• Allow butter to cool to room temperature before using; the refrigerator will speed the cooling process, but don't let it harden!
• Preheat the oven to 350 degrees.
• Grease an 8x8 baking pan with butter or line it with parchment paper. Set aside.
• Combine flour, baking powder, nutmeg, cinnamon, and brown sugar in a medium mixing bowl. Set aside.
• In a large mixing bowl, mix together egg, heavy cream, and butter. 
• Mix dry ingredients slowly into the wet ingredients until just incorporated.
• Add in chopped walnuts and white chocolate chips.
• Pour the batter into the 8x8 pan and spread it evenly.
• Bake for 30 minutes or until a toothpick comes out clean.