Lemon-Souffle Pudding Cake

Preparation Preheat oven to 325°. Butter a shallow 1 1/2–2-quart baking dish, then sprinkle with granulated sugar. Stir buttermilk, creme fraiche, lemon zest, and lemon juice in a medium bowl just to combine and set aside. Using an electric mixer on high speed, beat 4 tablespoons butter and 3/4 cup granulated sugar in a large bowl until well combined, about 4 minutes. Add egg yolks 1 at a time, beating to blend between additions and scraping down sides of bowl as needed. Reduce mixer speed to low and, with motor running, add reserved buttermilk mixture in 3 additions, alternating with flour in 2 additions, beginning and ending with buttermilk mixture (batter will be extremely loose). Using an electric mixer with clean, dry beaters, beat egg whites and salt on high speed in a medium bowl until soft peaks form. Fold egg whites into pudding cake batter in 3 additions, just barely blending after each addition. Scrape pudding cake batter into prepared baking dish and place on a rimmed baking sheet. Bake until top is puffed and golden brown and center barely jiggles, 35–45 minutes. Transfer baking dish to a wire rack and let pudding cake cool at least 30 minutes. Serve pudding cake dusted with powdered sugar and topped with blackberries, if desired. Do ahead:Pudding cake can be baked 1 day ahead. Cover and chill. Bring to room temperature before serving.

Preparation Preheat oven to 325°. Butter a shallow 1 1/2–2-quart baking dish, then sprinkle with granulated sugar. Stir buttermilk, creme fraiche, lemon zest, and lemon juice in a medium bowl just to combine and set aside. Using an electric mixer on high speed, beat 4 tablespoons butter and 3/4 cup granulated sugar in a large bowl until well combined, about 4 minutes. Add egg yolks 1 at a time, beating to blend between additions and scraping down sides of bowl as needed. Reduce mixer speed to low and, with motor running, add reserved buttermilk mixture in 3 additions, alternating with flour in 2 additions, beginning and ending with buttermilk mixture (batter will be extremely loose). Using an electric mixer with clean, dry beaters, beat egg whites and salt on high speed in a medium bowl until soft peaks form. Fold egg whites into pudding cake batter in 3 additions, just barely blending after each addition. Scrape pudding cake batter into prepared baking dish and place on a rimmed baking sheet. Bake until top is puffed and golden brown and center barely jiggles, 35–45 minutes. Transfer baking dish to a wire rack and let pudding cake cool at least 30 minutes. Serve pudding cake dusted with powdered sugar and topped with blackberries, if desired. Do ahead:Pudding cake can be baked 1 day ahead. Cover and chill. Bring to room temperature before serving.