1 cup (2 sticks) unsalted butter, room temperature, plus more for pans
1 and 3/4 cups sugar
4 large eggs, plus 2 large egg yolks, room temperature
1 tablespoon pure vanilla extract
3 cups cake flour
1 tablespoon baking powder
1/2 teaspoon salt
1 and 1/2 cups buttermilk, room temperature
2 cups raspberries
3 tablespoons confectioners' sugar
2 cups cold heavy cream
Preheat oven to 350 degrees. Lightly butter two 9-inch round cake pans (2 inches deep). Line bottoms with parchment paper; butter parchment.
In a large bowl, using and electric mixer, beat butter and sugar on high until light and fluffy, about 6 minutes. Beat in eggs and egg yolks, one at a time, until combined. Beat in vanilla extract.
In another large bowl, whisk together flour, baking powder, and salt. With mixer on low, add 1/3 the flour mixture to butter mixture, beating to combine. Beat in half the buttermilk, another 1/3 the flour mixture, remaining buttermilk, and remaining flour until just combined. Scrape down bowl as needed.
Divide batter between pans, firmly tap on a flat surface to remove air bubbles, and smooth tops. Bake until cakes are golden and puffed and a toothpick inserted in center comes out with a few moist crumbs attached, about 30 minutes, rotating pans halfway through. Let cakes cool in pans on wire racks 10 minutes. Run a knife around edges, then invert; remove parchment. Invert cakes again and let cool completely on wire racks.
In a medium bowl, gently mash 1 cup raspberries with a fork. Stir in 1 cup whole raspberries. In a large bowl, using an electric mixer, beat cream and confectioners' sugar on high until soft peaks form, 2 minutes. With a rubber spatula, gently fold raspberries into whipped cream.
Place 1 cake on a cake stand or serving plate. Spread raspberry cream on top, leaving a 1/2-inch border. Top with other cake, pressing gently, and finish with remaining raspberry cream.