- First, make the custard. Put the custard powder and 25g of the sugar in a small pan and whisk to combine. Pour in the milk and whisk until smooth. Put the pan over a medium heat and warm, whisking constantly, until the custard thickens and just starts to bubble. Add in 10g of the butter and mix until melted and combined. Scrape the custard into a small bowl, press a sheet of baking paper on the surface, and chill.
- In a small bowl, rub 40g of butter into the flour using your fingertips, stir in 30g caster sugar and bring together to form a soft dough. Cover and chill.
- Grease and line a loose-bottomed, deep, 23cm round cake tin. Heat the oven to 180°C/fan 160°C/gas 4.
- Put the remaining 175g butter and remaining 175g sugar in a large bowl and beat using an electric whisk for 5/10 minutes until light and fluffy, then add vanilla.
- In a separate bowl, sift together flour and baking powder. Add the eggs, one at a time, followed by a tablespoon of flour each time, beating until combined before adding another. Then stir in yogurt and remaining flour gradually.
- Scrape into the prepared cake tin and level the surface. Dollop the custard over the cake batter, then scatter over the rhubarb pieces. Break up the crumble and sprinkle over the rhubarb. Bake for 50 minutes or until golden and the cake is just pulling away from the sides of the tin.
- Delicious served warm or cold with natural yogurt and rhubarb compote