Clean and cut the rhubarb and strawberries into small pieces about the same size. Add the sugar and potato starch and stir to distribute. Transfer fruit mixture to a pyrex or ceramic tart pan.
Melt the butter and stir in the maple syrup and vanilla extract. Combine rolled oats, sugar and flour and pour butter mixture in. Stir to combine.
Transfer crisp batter over the fruits and gently spread all over. Bake in the preheated oven for 40 minutes at 180°C.
This strawberry rhubarb crisp tastes fantastic both warm and cold. It is easier to serve when cold.