Preheat the oven to 300F (150C). Place pecans on a parchment paper lined baking sheet and toast for 15 minutes.
Cool slightly and chop the pecans in smaller pieces.
Preheat the oven to 350F (180C). Grease three 8-inch (20cm) pans and line the bottom with parchment paper.
In a medium bowl combine the flour, cocoa powder, baking powder and salt.
In another bowl mix the oil and sugar until well combined. Add eggs, one at a time, vanilla extract and mix to combine.
Add sour cream and mix to combine. With the mixer on low, gradually add flour mixture. Make sure to not overmix the batter. Add the melted chocolate and chopped pecans and stir to incorporate.
Divide batter evenly into the prepared pans.
Bake for 10-13 minutes or until a toothpick inserted into the center comes out with a few crumbs.
Let them cool on the pan for about 5 minutes, then remove to a cooling rack to cool completely.