Preheat your oven to 350°F (175°C) and grease a 9×13-inch baking pan.
In a medium bowl, whisk together the flour, baking powder, baking soda, and salt.
In a separate large bowl, cream together the softened butter and granulated sugar until light and fluffy.
Add the eggs, one at a time, beating well after each addition. Stir in the vanilla extract.
Gradually add the dry ingredients to the wet ingredients, alternating with the sour cream, beginning and ending with the dry ingredients. Mix until just combined.
Step 2: Prepare the Pecan Topping
In a saucepan over medium heat, melt the unsalted butter.
Stir in the brown sugar and heavy cream until well combined.
Bring the mixture to a simmer, then remove from heat and stir in the chopped pecans and vanilla extract.
Step 3: Assemble and Bake
Pour the prepared cake batter into the greased baking pan, spreading it evenly with a spatula.
Pour the pecan topping over the cake batter, spreading it evenly.
Bake in the preheated oven for 30-35 minutes, or until a toothpick inserted into the center comes out clean.
Remove the cake from the oven and let it cool slightly before serving.
