Preheat oven to 180°C / 350°F (top & bottom heat)
Wash the rhubarb, cut into pieces and toss with a little sugar. Set aside
In a bowl, cream together butter and sugar until light and fluffy
Add eggs one at a time
Mix flour and baking powder, then add to the batter along with milk
Spread evenly onto a lined baking tray
Distribute the rhubarb on top
For the streusel, combine flour, sugar and butter with your hands until crumbly
Sprinkle generously over the cake
Bake for 35–40 minutes until golden
Let cool slightly — it's best when still a little warm
