If the rhubarb stems are large, cut them in half lengthwise. Then cut into 1cm pieces.
150 g rhubarb
Add the oats to the bowl of a food processor and blitz until powdery.
200 g porridge or instant oats
Cut the apples from the core, and chop roughly. Add to the oats and blitz again until very finely chopped.
2 dessert apples
Add the baking powder, 1 teaspoon vanilla, oil, honey and 2 eggs and blitz until thoroughly mixed.
1 teaspoon baking powder, 2 tablespoon olive oil, 1 teaspoon vanilla extract, 2 eggs, 2½ tablespoon honey
Stir in the rhubarb by hand.
Line the muffin tin with 6 paper cases. Spoon a rounded tablespoon of muffin mixture into each case and level out.
Add a heaped teaspoon of custard to the centre of each muffin.
Top with the remaining muffin mixture and gently smooth the mixture over the custard. The custard should be fully covered.
Bake at 180 degrees for 20 minutes until golden and set. Cool on a wire rack.