Preheat the oven to 350°F (175°C). Grease and flour a 9-inch round cake pan.
Combine dry ingredients: In a medium bowl, whisk together flour, baking powder, baking soda, and salt. Set aside.
Cream butter and sugar: In a large mixing bowl, beat softened butter and sugar together until light and fluffy (about 3-4 minutes).
Add eggs and vanilla: Beat in the eggs, one at a time, followed by vanilla extract.
Alternate adding dry ingredients and buttermilk: Gradually add the dry ingredients to the wet mixture, alternating with buttermilk. Begin and end with the dry ingredients.
Fold in pecans: Gently fold in toasted chopped pecans.
Bake: Pour the batter into the prepared pan and bake for 40-45 minutes, or until a toothpick inserted into the center comes out clean.
Cool: Allow the cake to cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.