Preheat your oven to 325°F (165°C/Gas Mark 3). Grease and flour, or use non-stick baking spray (with flour), a 10-inch bundt pan (12-cup or 3-quart bundt pan size).

Whisk together the dry ingredients (in a large mixing bowl or the bowl of your stand mixer), including 3 cups unbleached all-purpose flour, 2 cups white sugar, 1 tsp salt, 1 tsp baking powder, and ½ tsp baking soda in a large bowl. Then, in a second bowl, whisk together 1 cup buttermilk, 4 large eggs, and 2 tsp vanilla extract plus the optional 1 tsp spiced rum if desired. Set the wet ingredient mixture aside (it’s okay if the mixture begins to look curdled).

Blend in the softened 1 cup butter and half of the buttermilk mixture into the dry ingredients with an electric mixer or stand mixer on low speed. The mixture will get to a crumbly consistency in about a minute. Add the remaining buttermilk mixture, slowly drizzling into the crumbled mixture while your mixer is on low.

Once fully combined, beat the batter for 3 minutes on medium speed. Transfer into your prepared bundt pan.

Bake at 325°F (165°C/Gas Mark 3) for 1 hour or until a cake tester, knife, bamboo skewer, or toothpick inserted into the center of the cake comes out clean.

Start the butter sauce while the cake is baking and getting close to being done. Heat the ¾ cup sugar, 5 Tbsp butter, 3 Tbsp water, and 2 tsp vanilla extract in a saucepan over medium heat.

Bring the sauce to a boil then immediately reduce the heat and simmer. Stir for 1-2 minutes until the sugar is fully dissolved.

Remove the cake from the oven and place on a cooling rack.

Prick holes in the cake while it’s warm, just out of the oven, and still in the bundt pan. Use a bamboo skewer or toothpick to poke approximately 3-4 dozen holes about ¾ of the way through the cake.

Slowly pour or spoon the butter sauce glaze over the bottom of the cake until the glaze has sunk into the cake. If any of the butter glaze pools on the cake, poke more holes to help it sink in fully.

Leave the butter cake in the pan, on the cooling rack, before removing from pan. Let cool for about 30 minutes.

Turn the cake upside down onto a serving platter. Use a brush or spoon to evenly coat the remaining glaze over the cake's top and sides, allowing it to soak in as you apply it. (Take your time to apply the glaze gradually, allowing it to be absorbed).

Allow the thoroughly soaked butter cake to sit at room temperature for one hour before serving. When you're ready to serve, use a fine sieve to gently dust confectioners' sugar over the cake.