01 - Preheat oven to 350°F. Grease a 9-inch round cake pan and line with parchment paper.
02 - Combine rhubarb, strawberries, sugar, and lemon juice in a small bowl. Toss to coat evenly and set aside.
03 - Mix flour, sugar, almonds, salt, and cold butter in a bowl. Rub with fingertips until mixture resembles coarse crumbs. Refrigerate until ready to use.
04 - Whisk together flour, baking powder, baking soda, and salt in a medium bowl.
05 - Beat butter and sugar in a large bowl until light and fluffy. Add eggs one at a time, mixing well after each addition. Stir in lemon zest and vanilla extract.
06 - Add half the dry ingredients to the butter mixture, followed by buttermilk, then remaining dry ingredients. Mix until just combined.
07 - Spread batter evenly in prepared pan. Arrange fruit filling over batter. Sprinkle streusel topping evenly over fruit. Bake for 40 minutes until golden and a toothpick inserted in center comes out clean.
08 - Let cake cool in pan for 15 minutes. Remove from pan and transfer to wire rack to cool completely before slicing.