For the cake:

1. Preheat & prep. Preheat the oven to 325°F. Generously spray a 10-cup bundt pan with baking spray or grease well with butter (hitting every corner for a flawless release!), and then set aside. In a medium bowl, combine the flour, baking powder, and salt and whisk well to combine. Set the dry ingredients aside while you brown the butter. 
2. Brown the butter. In a small, light-colored saucepan, melt the butter over medium heat. Once the butter melts, it will get foamy and you will hear it bubbling as it cooks. Then it will take on a clear, light golden color. Note: Do not leave the pot unattended for long during the browning process as it can burn very quickly. Stir the butter every so often, scraping up any bits as you stir, until it turns deep brown and has a nutty aroma with brown bits on the bottom. Once achieved, remove from heat and let brown butter cool down.
3. Bring cake batter together. In a large bowl, combine the brown butter, oil, granulated sugar, brown sugar, eggs, vanilla essence, rum extract (if using), and buttermilk. Whisk the wet ingredients well to thoroughly combine. Then add the flour mixture into the same bowl and use a spatula to fold the dry ingredients into the wet until just combined with all dry ingredients dissolved. Empty the cake batter into the prepared bundt pan- use a utensil to smooth the top if needed.
4. Bake the cake for 1 hour or until a toothpick inserted into the center of the cake comes out clean. Allow the cake to cool in the pan for 15 minutes. Then carefully invert the cake onto a wire rack to continue cooling. Allow the cake to cool down completely before icing.

For the caramel sauce:

1. Make caramel sauce. In a medium saucepan over medium heat, combine the brown sugar, butter, and salt. Let the mixture simmer, stirring every so often, until the sugar has dissolved, about 3-4 minutes. Then add the cream and whisk well to fully combine. Bring the mixture to a gentle simmer, lower the heat if necessary. Cook the sauce, whisking occasionally, until the caramel sauce thickens some, about 6-7 minutes. Then remove from heat and add the vanilla essence, stirring well to combine. Let caramel sauce cool down to room temperature before glazing over the cake- it will thicken as it cools.
2. Glaze cake & serve. Place cake onto a cake stand or large plate/platter and pour desired amount of homemade caramel sauce over the cake. Slice into wedges and serve. If desired, this cake is really good with a scoop of vanilla ice cream or a dollop of whipped cream. Enjoy!