In a skillet over medium heat, melt 3 tablespoons of butter. Add chopped pecans and cook, stirring occasionally, until toasted, about 5 to 8 minutes. Transfer the toasted nuts to a small bowl and let cool completely.

Preheat the oven to 350°F. Grease 3 (9-inch) round cake pans with baking spray and line the bottoms with parchment paper.

In a large bowl, whisk together the flour, baking powder, baking soda, and salt.

In a mixing bowl, beat the remaining 1¼ cups butter and granulated sugar together until light and fluffy, about 3 to 4 minutes.

Add the eggs one at a time, beating until combined. Beat in the vanilla.

With the mixer on low speed, alternate adding the flour mixture and buttermilk until fully combined. Fold in the cooled buttered pecans. Divide among the prepared cake pans.

Bake for 25 to 30 minutes, or until a pick comes out with bits. Let cool for 20 minutes in pans before inverting onto racks to cool completely.

In a mixing bowl, beat the butter, cream cheese, and salt on medium speed until creamy, about 1 minute.

Gradually add powdered sugar while mixing on low speed. Scrape down the bowl and beat in cream and vanilla. Increase speed to medium-low and beat until smooth, about 1 minute.

Place one cooled cake layer on a plate. Top with 1 cup frosting. Repeat with another layer. Top with the final layer and spread remaining frosting over the cake. Press chopped pecans around the bottom and sprinkle remaining on top. Chill for 30 minutes.