Heat the oven to 190C (180C fan)/gas 6. Spread out the rhubarb pieces in a single layer in a 30cm ovenproof pan or gratin dish. Sprinkle with the sugar, then cover with the orange zest and juice.
Put in the oven for 10 to 12 minutes, until it just begins to feel tender to the touch, then leave to cool.
Meanwhile, blitz the eggs, egg yolk, sugar, cream and milk with a hand blender or whisk, then fold in the flour and almonds, along with a small pinch of salt.
Pour this batter over the cooled rhubarb, then put in the oven for 35-45 minutes, until it is set with a slight wobble in the middle.
Eat warm or at room temperature with a little extra cream.