1-Begin by preheating the oven to 350 degrees Fahrenheit and preparing a 9-inch springform pan by buttering the bottom, lining it with parchment paper, and lightly greasing the sides. In a mixing bowl, beat the eggs and sugar on high speed for 5 minutes until thick and pale, then stir in the olive oil for a smooth mixture.

2-Next, in a separate bowl, whisk together the flour and baking powder. Add half of this dry mixture to the batter and mix on low speed just until combined, followed by the lemon zest and vanilla extract. Slowly mix in the seltzer water or club soda on low speed, avoiding overmixing, then incorporate the remaining flour mixture.

3-Transfer the batter to the prepared pan and spread it evenly, then evenly distribute the mixed berries over the top. For the crumb topping, combine the flour, sugar, salt, and butter in a bowl and rub together with your fingertips until coarse crumbs form, then sprinkle it over the cake. Bake for 45 to 50 minutes until golden brown and a toothpick inserted in the center comes out clean, taking care not to overbake.