Place the aubergines on two baking trays lined with baking paper, brush both sides with oil, season with salt.
Bake for approx. 20 mins. in the oven preheated to 200 °C (convection).
Puree the cream, milk, cornflour and cheese, season. Pour half of the sauce into the prepared dish. Layer the potatoes and sage on top of the sauce along with the aubergines. Pour the remainder of the sauce over the top.
Approx. 40 mins. in the centre of an oven preheated to 200°C. Remove and leave to stand for approx. 5 mins.