Place 1/2 cup unsalted butter in a small pot over low-medium heat. Heat the butter until it melts and begins to bubble and foam. Keep heating over low heat, stirring frequently, until the bubbles stop and the butter has turned a brown color and is emitting a nutty smell.
Place the butter in a bowl and place in the fridge for about 60 minutes. Remove the butter from the fridge and use a spoon to stir it. Allow it to spend the next 10 minutes or so coming to room temperature (your butter should be about 68 degrees Fahrenheit internally before you begin the next steps of the frosting).
In a large mixing bowl, use an electric hand mixer to beat together the butter and softened 8 oz cream cheese until smooth. Add the 1 1/2 tsp vanilla and the 1/4 tsp salt and beat again until combined.
Add the 3 1/2 cups powdered sugar about 1 cup at a time, beating between each addition.
Pipe onto cupcakes, cookies, cakes, etc. Enjoy!