Preheat oven to 350 degrees F. Grease and flour 2 9x2-inch round baking pans; set aside. In a medium bowl sift together the flour, baking powder, and salt. In a very large mixing bowl beat the sugar and butter with an electric mixer on medium to high speed for 6 to 8 minutes or until very light and fluffy. Add eggs and yolks, one at a time, beating until combined after each addition. Beat in the vanilla. Add flour mixture to beaten mixture in 3 additions, alternating with buttermilk. Divide batter between prepared pans, filling each about 1/2 full (about 3 1/4 cups batter in each). Spread batter evenly in pans.
Bake about 35 minutes or until a toothpick inserted near the centers comes out clean. Remove and cool in pans on a wire rack for 10 minutes. Remove from pans and cool completely. Frost with ganache. Sprinkle with sea salt.
Salted Dark Chocolate Ganache
Place chocolate in a large heat-proof mixing bowl. In a medium saucepan bring cream just to boiling. Pour cream over chocolate. Let stand without stirring for 2 minutes. Stir to melt chocolate. Stir in the salt. Set bowl in a larger bowl with ice water for 15 to 20 minutes, stirring occasionally, or until cool. Beat with an electric mixer on medium speed for 2 minutes or until light and fluffy. Spread over cake layers.