PreparationFor buttermilk cake: Preheat oven to 350°F. Butter and flour pan. Whisk baking soda, salt, and 2 cups flour in a medium bowl; set aside. Preheat oven to 350°F. Butter and flour pan. Whisk baking soda, salt, and 2 cups flour in a medium bowl; set aside. Using an electric mixer, beat sugar and 1 1/4 cups butter in another medium bowl until light and fluffy, about 4 minutes. Add eggs one at a time, beating to blend between additions and scraping down sides of bowl. Reduce mixer speed to low and, with motor running, add dry ingredients in 3 additions alternating with buttermilk in 2 additions, beginning and ending with dry ingredients. Scrape batter into prepared pan. Bake until cake is golden and a tester inserted into the center comes out clean, 40-45 minutes. Transfer pan to a wire rack and let cake cool before turning out. DO AHEAD: Cake can be made 2 days ahead. Store tightly wrapped at room temperature. For sour milk jam: Bring milk and sugar to a boil in a small saucepan over medium heat, stirring to dissolve sugar; reduce heat and simmer gently, whisking occasionally, until mixture measures a scant 1/4 cup, 20-25 minutes. Transfer to a small bowl; let cool (it will thicken as it sits). Whisk in crème fraîche, cover, and chill. DO AHEAD: Jam can be made 2 days ahead. Keep chilled. For gin-poached cherries and assembly: Bring cherries, gin, sugar, juniper berries, and 1 cup water to a boil in a medium saucepan; reduce heat and simmer until liquid is syrupy, 6-8 minutes. Let cool. Spoon a few dollops of jam onto plates. Tear cake into pieces and arrange around jam. Top with cherries and fennel fronds. DO AHEAD: Cherries can be poached 3 days ahead. Cover and chill.
PreparationFor buttermilk cake: Preheat oven to 350°F. Butter and flour pan. Whisk baking soda, salt, and 2 cups flour in a medium bowl; set aside. Preheat oven to 350°F. Butter and flour pan. Whisk baking soda, salt, and 2 cups flour in a medium bowl; set aside. Using an electric mixer, beat sugar and 1 1/4 cups butter in another medium bowl until light and fluffy, about 4 minutes. Add eggs one at a time, beating to blend between additions and scraping down sides of bowl. Reduce mixer speed to low and, with motor running, add dry ingredients in 3 additions alternating with buttermilk in 2 additions, beginning and ending with dry ingredients. Scrape batter into prepared pan. Bake until cake is golden and a tester inserted into the center comes out clean, 40-45 minutes. Transfer pan to a wire rack and let cake cool before turning out. DO AHEAD: Cake can be made 2 days ahead. Store tightly wrapped at room temperature. For sour milk jam: Bring milk and sugar to a boil in a small saucepan over medium heat, stirring to dissolve sugar; reduce heat and simmer gently, whisking occasionally, until mixture measures a scant 1/4 cup, 20-25 minutes. Transfer to a small bowl; let cool (it will thicken as it sits). Whisk in crème fraîche, cover, and chill. DO AHEAD: Jam can be made 2 days ahead. Keep chilled. For gin-poached cherries and assembly: Bring cherries, gin, sugar, juniper berries, and 1 cup water to a boil in a medium saucepan; reduce heat and simmer until liquid is syrupy, 6-8 minutes. Let cool. Spoon a few dollops of jam onto plates. Tear cake into pieces and arrange around jam. Top with cherries and fennel fronds. DO AHEAD: Cherries can be poached 3 days ahead. Cover and chill.