01 - Preheat oven to 350°F. Grease and line a 9-inch round cake pan with parchment paper.
02 - Toss rhubarb and strawberries with 2 tablespoons sugar and lemon juice in a small bowl. Set aside.
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 bowl.
05 - Beat butter and sugar in a large bowl until light and fluffy. Add eggs one at a time, mixing well after each. Stir in lemon zest and vanilla.
06 - Add half of the dry ingredients to the wet mixture, followed by buttermilk, then remaining dry ingredients. Mix until just combined.
07 - Spread batter evenly into prepared pan. Scatter rhubarb and strawberries over batter. Sprinkle streusel over the top.
08 - Bake for 40 minutes until a toothpick inserted in the center comes out clean and top is golden.
09 - Cool in pan for 15 minutes, then remove and cool completely on a wire rack. Slice and serve.