The addition of buttermilk makes this guilt-free cake the perfect combination of sweet and tart! For a more indulgent experience, top cake slice with real whipped cream or vanilla ice cream!
Preheat oven to 400°F (200°C). Line a baking sheet with parchment paper. Grease an 8 x 8 x 2-inch deep (20 x 20 x 5 cm) baking dish; set aside.
Toss together strawberries, rhubarb and sugar. Spread onto prepared baking sheet. Roast for 30 minutes or until golden. Remove from oven and reduce oven temperature to 350°F (180°C).
Cake: Meanwhile, in a medium bowl, whisk together flour, sugar, baking powder, baking soda and salt. In a small bowl, whisk together buttermilk, egg and vanilla. Pour into flour mixture and add butter. Stir to combine. Spread into prepared baking dish. Sprinkle roasted fruit mixture over top evenly. Bake for about 50 minutes or until cake is golden and cake tester comes out clean. Let cool slightly.
Cut cake and serve with whipped cream or vanilla ice cream.
Keep any leftover cake in refrigerator for up to 5 days or freezer for up to 2 weeks.
You can also use an 11 x 7 inch (28 x 18 cm) baking dish to bake this cake. If using this pan decrease the baking time by about 10 minutes.