Wash the strawberries and rhubarb and drain well. Then clean and cut into very small cubes, no more than 0.5 cm in length.
Preheat the oven to 180 degrees top / bottom heat. Butter the muffin tin and sprinkle with ground nuts or almonds. Or use 2 paper baking cases for each well.
For the crumble, knead the butter, sugar, flour, nuts and cinnamon together well and rub in until crumbly.
Mix the flour, baking powder, baking soda and nuts. In another bowl, beat the egg lightly and mix well with the sugar, vanilla flavor, oil, buttermilk and the rhubarb pieces. Now fold in the flour mixture with a whisk, but only stir until everything is moist. Finally, carefully fold in the strawberry pieces.
Now quickly pour 3/4 of the batter into the prepared muffin pan. Sprinkle on the sprinkles.
Bake on the middle shelf at 180 degrees for about 20-25 minutes.
Allow to cool after baking and sprinkle with powdered sugar.
Alternatively, bake the muffins with ground hazelnuts in the batter and the crumble.