Heat oven to 350°F. In a large bowl, cream the butter and sugar with a hand blender (or in the bowl of a stand mixer), at medium-high speed for 3 minutes, until lightened in color. Add the flour, baking powder, salt, and eggs, and beat at medium speed 1 minute, scraping down the sides of the bowl once. Spread the batter evenly into an 8-inch springform pan. Place blueberries and strawberries on top of the batter, pressing lightly into the surface. Drizzle lemon juice evenly over the top.
Bake 1 hour or until golden. Remove and allow to cool slightly in the pan, about 30 minutes. Run a knife around the edges, and remove sides of the pan. Top with powdered sugar or freshly whipped cream to serve.
How to Celebrate Anything by Jenny Rosenstrach. Copyright 2016 by Jenny Rosenstrach. Reprinted by arrangement with Ballantine Books, an imprint of Random House, a division of Penguin Random House LLC. All rights reserved.