Preheat the oven to 350˚F (175°C). Line an 8 inch (20cm) square baking pan with baking parchment and grease. Set aside.

Start with the streusel: In a medium bowl mix flour with brown sugar and salt. Add the melted butter and mix with a fork until crumbs form. Place in the fridge.

For the filling cut the rhubarb and strawberries into small pieces. Place in a bowl and add brown sugar and flour – mix until all is well combined and rhubarb and strawberries are covered evenly.

For the batter add the butter in small pieces and the confectioner’s sugar in a large bowl. Beat on high speed for about 3 minutes until light and fluffy. Add the eggs one at a time and mix well after each addition. Add the vanilla extract and mix well. Mix flour, baking powder and salt and add to the bowl. Mix until just combined. Transfer the batter to the prepared baking pan and spread evenly. Sprinkle with the rhubarb/strawberry mixture and top with the streusel.

Bake for 45-50 minutes or until the top is golden and a toothpick inserted in center comes out clean. Let cool completely in pan. Using paper overhang, lift cake from pan. Cut into bars.