Preheat the Oven: Start by preheating your oven to 350°F (175°C). Grease and flour a 9-inch round or square cake pan.
Mix Dry Ingredients: In a medium bowl, whisk together the all-purpose flour, baking powder, baking soda, and salt. Set aside.
Cream Butter and Sugar: In a large bowl, beat the softened butter and granulated sugar together using an electric mixer on medium speed until light and fluffy (about 3-4 minutes).
Add Eggs and Vanilla: Add the eggs one at a time, mixing well after each addition. Then, stir in the vanilla extract.
Alternate Dry Ingredients and Wet Ingredients: Add the flour mixture in three parts, alternating with the sour cream and buttermilk. Start and end with the dry ingredients. Mix just until combined.
Bake: Pour the batter into the prepared cake pan and smooth the top. Bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean. Let the cake cool in the pan for 10 minutes, then transfer it to a wire rack to cool completely.
Cook the Praline Sauce: In a medium saucepan, combine the brown sugar, butter, and heavy cream. Bring to a simmer over medium heat, stirring constantly, until the mixture thickens and becomes smooth (about 5 minutes).
Add Pecans and Vanilla: Stir in the chopped pecans and vanilla extract. Continue to cook for another 2 minutes.
Top the Cake: Pour the hot praline topping over the cooled cake, allowing it to spread and cover the entire surface. Let it sit for a few minutes to set.