In a small saucepan, add butter and melt over medium heat. Once the butter has fully melted, a white foam will begin to appear over the top of the butter.
Watch carefully as the butter’s color changes to brown and the smell of the butter becomes somewhat nutty.
As soon as the butter is an amber brown color, remove from heat and cool in the refrigerator until it the butter has become solid again (can take 1-2 hours so I sometimes do this the night before baking the cake).
Once butter is solid, preheat oven to 325 degrees then liberally spray 10 cup bundt pan with non-stick baking spray.
In your mixer bowl, add butter and shortening and beat for 2 minutes on high speed. Slowly add in sugar beat on high speed for an additional seven minutes until very pale yellow and fluffy.
Next, add eggs, one at a time, combining well after each addition and scraping down the sides as needed.
Turn your mixer down to its lowest speed, and slowly add flour into batter in two increments then add salt, baking powder and baking soda. Be careful not to overbeat.
Lastly, pour in buttermilk and vanilla extract, scrape down sides and mix until just combined and turn off mixer.
Add batter to prepared cake pan and bake for 45-55 minutes or until toothpick inserted into center comes out mostly clean but still moist. While cake is baking, work on the butter sauce below.