Vanilla-Buttermilk Cake With Raspberries and Orange Cream-Cheese Frosting

Ingredients:
Nonstick vegetable oil spray
2 cups cake flour
1 teaspoon baking powder
1/2 teaspoon baking soda
1/4 teaspoon kosher salt
3/4 cup (1 1/2 sticks) unsalted butter, room temperature
1 3/4 cups granulated sugar, divided
4 large eggs, separated
1 teaspoon vanilla extract
1 cup buttermilk
1/4 cup granulated sugar
1 vanilla bean, split lengthwise
2 (8-ounce) packages cream cheese, chilled
10 tablespoons unsalted butter, room temperature
1 teaspoon finely grated orange zest
1 tablespoon fresh orange juice
1 teaspoon vanilla extract
3/4 cup powdered sugar, sifted
6 ounces raspberries, divided
Edible flowers (for garnish; optional)
A 10-inch round cake pan

Instructions:
Place a rack in middle of oven; preheat to 350°F. Lightly coat cake pan with nonstick spray and line bottom with parchment paper. Whisk flour, baking powder, baking soda, and salt in a medium bowl; set aside.
Using an electric mixer on medium-high speed, beat butter and 1 1/2 cups granulated sugar in a large bowl, scraping down sides of bowl as needed, until light and creamy, about 5 minutes. Add egg yolks in 2 additions, scraping down bowl after each. Beat in vanilla.
Reduce mixer speed to low, then add dry ingredients in 2 additions alternately with buttermilk in 2 additions, scraping down sides of bowl as needed.
Using electric mixer on medium speed, beat egg whites in another large bowl until soft peaks form, 2–3 minutes. Slowly add remaining 1/4 cup granulated sugar and continue to beat until stiff, glossy peaks form, about 3 minutes more. Fold half of the egg whites into flour mixture, then gently fold in remaining egg whites.
Scrape batter into prepared pan; smooth surface. Bake, rotating pan halfway through and covering with foil during the last 15 minutes of baking, until golden brown, firm to the touch, and a tester inserted into the center comes out clean, 45–50 minutes. Transfer pan to a wire rack and let cake cool.
Combine granulated sugar and 1/4 cup water in a medium saucepan. Scrape in vanilla seeds, add pod, and stir to combine. Bring to a boil, cover, and steep at least 15 minutes. Set aside to cool. Discard pod before using.
Using electric mixer on medium-high speed, beat cream cheese and butter in a large bowl until smooth, about 1 minute. Beat in orange zest, orange juice, and vanilla. Reduce mixer speed to medium and beat in powdered sugar, scraping down bowl as needed, until light and fluffy, 2–3 minutes.
Run a knife around sides of cooled cake and invert onto a wire rack; remove parchment.
Spread 1 Tbsp. frosting in the center of a platter. Place cake, top side down, in the center. Using a pastry brush, brush 3 Tbsp. vanilla syrup over top of cake; reserve remaining syrup for another use. Spread 1 cup frosting evenly over top and sides to create a crumb coat. Chill 30 minutes to let frosting set. Frost top and sides, swirling decoratively; reserve remaining frosting for another use.
Chill at least 30 minutes or up to overnight to let frosting set. Before serving, top cake with 3 oz. raspberries and edible flowers, if using. Serve remaining 3 oz. raspberries alongside.
Cake can be made 3 days ahead; wrap tightly in plastic and chill, or freeze up to 2 weeks. Syrup can be made 5 days ahead; store in an airtight container and chill. Frosting can be made 3 days ahead; cover with plastic wrap, pressing directly on surface, and chill. Bring to room temperature before using.