Melt 2 tbsp butter in a skillet, add pecans and toast 4–5 minutes until fragrant and a shade darker. Cool completely.
Heat oven to 350°F (175°C). Grease and line two 8 or 9-inch round pans.
Brown 1/2 cup butter until golden with toffee smell. Pour into a bowl and chill about 1 hour until soft-solid.
Whisk flour, baking powder, baking soda and salt.
Beat softened butter with brown and white sugar 3–4 minutes until pale and fluffy.
Beat in eggs one at a time, then vanilla.
On low, add flour mix in three parts alternating with buttermilk. Mix only until no dry streaks remain.
Fold in 1 cup toasted pecans.
Divide batter between pans. Bake 25–35 minutes until a toothpick has a few moist crumbs. Cool 10 minutes, then turn out and cool completely.
Beat cream cheese and firmed brown butter until smooth. Add powdered sugar, vanilla and salt and beat 2 minutes.
Frost between layers and over the cake. Top with remaining pecans. Chill 30 minutes before slicing.
