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!