Preheat the oven to 350℉, and line an 8X12 inch oven-safe pan, then grease and set aside.
Sift both flour, baking powder, salt and set aside.
1¼ cup All-purpose flour, ½ teaspoon Salt, 1½ teaspoon Baking powder, 1 cup Almond flour
Use the paddle attachment and beat the butter and sugar for a few minutes until it is creamy and light.
1 cup Butter, 1 cup Sugar
Add the eggs one at a time and beat well after each on. Add vanilla extract and lemon zest (if using)
2 Eggs, 2 teaspoon Vanilla extract, 1 tablespoon Lemon zest
Add the sour cream and mix well. The mixture will look curdled, but it is okay.
¼ cup Sour cream
Use a rubber spatula to fold in the dry ingredients. Gently mix them all.
Mix in the chopped rhubarb and strawberries, and gently mix.
½ pound Rhubarb, 1 cup Strawberries
Scoop the batter into the prepared pan and spread evenly. Place the sliced rhubarb and strawberries on top and sprinkle the extra tablespoon sugar.
1 tablespoon Granulated sugar, ½ cup Sliced Rhubarb and strawberries for decorating the top
Bake for 45-50 minutes, then place the pan on the cooling rack. After 15 minutes, lift the parchment paper from the sides and transfer it to the cooling rack.