This strawberry rhubarb crumb cake is the perfect way to use up extra fruit from your garden!
In a large bowl, combine the rhubarb, strawberries, sugar, and flour. Toss to coat evenly. Set aside to let the juices release.
Preheat oven to 350°F. Line a 13x9-inch cake pan with parchment paper and set aside.
Melt the butter in a medium saucepan over medium heat. Add the brown sugar, vanilla, and salt and stir with a rubber spatula.
Add the flour and stir with the rubber spatula until everything is very well mixed and large, coarse crumbs form. Set aside.
Place the softened butter and sugar in the bowl of a stand mixer. Beat with the whisk attachment on medium-high speed until light and fluffy, about 5 minutes, scraping down the sides of the bowl as needed.
Add the eggs, one at a time, beating well between each addition and scraping down the sides of the bowl as needed. Add the sour cream, lemon zest, and vanilla and beat until well combined.
In a separate medium mixing bowl, whisk together the flour, baking powder, baking soda, and salt. Add the flour mixture to the cake batter and beat on low speed just until combined. It's okay if the batter is a little lumpy and there are a few bits of unmixed flour.
Spread the cake batter in the prepared cake pan and smooth the top with an offset spatula. Pour the fruit filling (including the juices) on top of the cake batter and spread out evenly. Add the crumb topping and use your fingers to distribute it evenly on top.
Put a baking tray on the rack under the cake pan to catch any spillovers. Bake in preheated oven for 1 hour and 10 minutes, or until the cake is golden brown and doesn't jiggle at all when you shake the pan. Make sure to bake this cake long enough because all the fruit makes it take longer for the cake to set!
Cool on a wire rack for at least 45 minutes before serving. This allows the cake to have time to absorb some of the liquid from the fruit.
Serve with vanilla ice cream or a dollop of whipped cream.