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.
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 - In a separate large bowl, beat butter and sugar 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, followed by buttermilk, then the remaining dry mixture. Mix until just combined.
07 - Spread cake batter evenly into the prepared pan. Scatter rhubarb and strawberries evenly over the batter. Sprinkle streusel over the top.
08 - Bake for 40 minutes, or until a toothpick inserted in the center comes out clean and the top is golden.
09 - Cool in the pan for 15 minutes, then remove from pan and cool completely on a wire rack. Slice and serve.