01 - Preheat oven to 350°F. Grease and line a 9-inch round cake pan with parchment paper.
02 - In a small bowl, toss rhubarb and strawberries with 2 tbsp sugar and lemon juice. Set aside to macerate.
03 - Combine flour, sugar, almonds, salt, and cold butter in a bowl. Rub with fingertips until mixture resembles coarse crumbs. Refrigerate until needed.
04 - Whisk together flour, baking powder, baking soda, and salt in a medium bowl.
05 - In a separate large bowl, beat butter and sugar until light and fluffy. Add eggs one at a time, mixing well after each addition. Stir in lemon zest and vanilla.
06 - Add half of the dry ingredients to the wet mixture, followed by buttermilk, then remaining dry mixture. Mix until just combined, being careful not to overmix.
07 - Spread cake batter evenly into the prepared pan. Scatter rhubarb and strawberries over the batter. Sprinkle streusel topping evenly over the fruit. Bake for 40 minutes until a toothpick inserted in the center comes out clean and top is golden.
08 - Cool in the pan for 15 minutes, then remove from pan and cool completely on a wire rack. Slice and serve.