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 tbsp sugar and lemon juice in a small bowl. 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 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.
06 - Add half of the dry ingredients to the wet mixture, followed by buttermilk, then remaining dry mixture. Mix until just combined.
07 - Spread batter evenly into prepared pan. Scatter rhubarb and strawberries over batter. Sprinkle streusel over the top. Bake for 40 minutes until toothpick inserted in center comes out clean and top is golden.
08 - Cool in pan for 15 minutes, then remove and cool completely on a wire rack. Slice and serve.