• Preheat an oven to 350°F (180°C). Grease a 9-inch (23-cm) round cake pan, line the bottom of the pan with parchment paper, then grease the parchment.
• In a medium bowl, whisk together the flour, both sugars, the baking powder, and salt.
• In a large bowl, whisk together the olive oil, milk, eggs, and lemon zest, then whisk in the flour mixture until combined. Using a rubber spatula, fold in the peach slices and blueberries.
• Pour the batter into the prepared pan. Bake until a toothpick inserted into the center of the cake comes out clean, about 1 hour.
• Transfer the pan to a wire rack and let cool 10 minutes, then invert the cake onto the rack and let cool completely.

Kefir Cream Frosting and Jam Topping

• In a large bowl with an electric mixer, whisk together softened butter until smooth. Slowly add in vanilla extract and whole milk kefir and mix until smooth.
• Turn the mixer to low speed and slowly add in powdered sugar (1/2 cup at a time) until blended well. If needed, add more whole milk kefir to get a smoother consistency.
• Use a spoon or a knife to smear the frosting.
• Spread jam of choice over the frosting.