Prep: Preheat your oven to 350°F (175°C). Grease and flour a 9×13 inch baking pan, or line it with parchment paper.

Combine Dry Ingredients: In a medium bowl, whisk together the flour, baking powder, baking soda, and salt. Set aside.

Cream Butter and Sugar: In a large bowl, using an electric mixer, cream the softened butter and sugar together on medium-high speed for 3-4 minutes, until the mixture is light, pale, and fluffy.

Add Eggs and Vanilla: Add the eggs one at a time, beating well after each addition until the yolk is fully incorporated. Scrape down the sides of the bowl. Beat in the vanilla extract.

Combine Wet and Dry: With the mixer on low speed, add the dry ingredients and the buttermilk alternately to the butter mixture, beginning and ending with the dry ingredients. Mix until just combined after each addition. Do not overmix.

Bake: Pour the batter into the prepared pan and spread it evenly. Bake for 30-40 minutes, or until a wooden skewer or toothpick inserted into the center of the cake comes out clean.

Cool: Let the cake cool in the pan on a wire rack for at least 20-30 minutes before serving.

Combine Ingredients: In a medium, heavy-bottomed saucepan, combine the butter, sugar, buttermilk, and corn syrup.

Bring to a Boil: Cook over medium heat, stirring constantly, until the butter melts and the sugar dissolves. Bring the mixture to a rolling boil.

Add Baking Soda: Once boiling, remove the pan from the heat and immediately whisk in the baking soda and vanilla extract.

Serve: The sauce is ready! It will be thin but will thicken slightly as it cools.

Warm Cake, Warm Sauce: For the ultimate experience, serve a square of the warm (or room temperature) cake with a generous pour of the warm buttermilk sauce over the top.

À la Mode: Take it to the next level by adding a scoop of high-quality vanilla ice cream.