Lightly grease a shallow ovenproof dish. Whisk together the eggs and sugar until pale, frothy and tripled in volume. Sift the flour into the bowl and lightly fold in. Add the cream, milk and vanilla extract and mix until just combined.
Pour into the ovenproof dish and place in a preheated oven, 190°C (375°F), Gas Mark 5, for 5 minutes until the surface is just starting to set. Scatter over the prunes, then return to the oven for a further 15–20 minutes until the clafoutis is risen and golden.