Ingredients:
For the vanilla butter cake:
- 1 1/2 cups all-purpose flour
 - 1 1/2 tsp baking powder
 - 1/4 tsp salt
 - 1/2 cup unsalted butter, softened
 - 1 cup granulated sugar
 - 3 large eggs
 - 1 tsp vanilla extract
 - 1/2 cup whole milk
 
For the buttermilk sauce:
- 1/2 cup unsalted butter
 - 1 cup granulated sugar
 - 1/2 cup buttermilk
 - 1 tsp vanilla extract
 - 1/2 tsp baking soda
 
Instructions:
1. Make the Cake:
- Preheat your oven to 350°F (175°C). Grease and flour an 8-inch round cake pan or a 9×9-inch square baking dish.
 - In a medium bowl, whisk together the flour, baking powder, and salt. Set aside.
 - In a large bowl, cream the softened butter and sugar together with an electric mixer on medium speed until light and fluffy (about 3-4 minutes).
 - Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.
 - Add the dry ingredients in three parts, alternating with the milk. Start and end with the dry ingredients. Mix each addition until just combined.
 - Pour the batter into the prepared cake pan and smooth the top.
 - Bake in the preheated oven for 25-30 minutes, or until a toothpick inserted into the center comes out clean.
 - Remove the cake from the oven and let it cool in the pan for 10 minutes before transferring it to a wire rack to cool completely.
 
2. Make the Buttermilk Sauce:
- While the cake is baking, prepare the buttermilk sauce. In a medium saucepan, melt the butter over medium heat.
 - Add the sugar, buttermilk, and vanilla extract, stirring to combine. Bring the mixture to a boil.
 - Once it begins to boil, reduce the heat and stir in the baking soda. Let the sauce simmer for 3-4 minutes, stirring occasionally, until it thickens slightly.
 - Remove the saucepan from the heat and set aside.
 
3. Serve:
- Once the cake has cooled, slice it into squares or wedges.
 - Drizzle the warm buttermilk sauce over the cake just before serving.
 
This Classic Vanilla Butter Cake with Buttermilk Sauce is incredibly moist, with a delightful balance of sweetness and richness from the sauce. The buttermilk sauce soaks into the cake and adds a luscious, velvety texture. Enjoy!