Preheat your oven to 325°F (163°C). Grease two 8-inch round cake pans with sides at least 2 inches high and line the bottoms with parchment paper. Lightly dust the sides with flour, then tap out any excess. Set the pans aside.

Prepare the cherry cake batter: In a medium bowl, whisk together the flour, baking powder, baking soda, and salt until well combined. Set aside. In a large bowl, combine the butter, vegetable oil, and sugar. Using an electric mixer with the paddle attachment, cream the mixture on medium speed for 2 to 3 minutes, until light and fluffy. (If mixing by hand, whisk vigorously for 3 to 4 minutes.)

Add the eggs one at a time, beating well after each addition. Stir in the vanilla extract until fully incorporated.

Alternately add the dry ingredients and the sour cream and buttermilk to the wet mixture, beginning with about one-third of the dry ingredients, followed by the sour cream, then another third of the dry ingredients, the buttermilk, and finally the remaining dry ingredients. Be careful not to overmix.

Gently fold the chopped cherries into the batter. Divide the batter evenly between the prepared pans.

Bake the cakes on the center rack of your oven for 30 to 35 minutes, or until a toothpick inserted into the center comes out clean or with just a few moist crumbs attached.

Let the cakes cool in the pans for 10 minutes, then carefully invert them onto wire racks to cool completely to room temperature before frosting.

Make the cherry swirl frosting: In a large bowl, beat the butter with an electric mixer (using the paddle or whisk attachment) on medium speed until smooth and creamy, about 2 minutes. Add the powdered sugar, salt, 5 tablespoons of milk, and vanilla extract. Mix on low speed until combined, then increase to medium speed and whip for 2 to 3 minutes, until the frosting is light, fluffy, and smooth. If the frosting is too thick, add more milk one tablespoon at a time until the desired consistency is reached.

Assemble the cake: Place one cooled cake layer on a serving plate or cake stand. Spread a generous layer of frosting over the top and sprinkle with fresh chopped cherries if desired. Place the second cake layer on top and frost the entire outside of the cake with the remaining frosting. For added decoration and flavor, spread cherry jam around the sides of the cake to create a beautiful swirl effect.

Chill the assembled cake for at least 1 hour before slicing and serving. This cake is best enjoyed slightly chilled but not straight from the refrigerator for the best texture and flavor.