Put the sugar, cream and butter in a wide saucepan. Cut the vanilla pod lengthwise, scrape out the pulp. Add the vanilla pod and pulp to the pot. Let the sugar-cream boil down for 40-45 minutes at low to medium heat, stirring occasionally, until the mixture is light brown and thick.
Remove the vanilla pod. Pinch the aluminium foil to form a firm strip and limit the baking tray to an area of approx. 20x20 cm. Brush the tray and foil well with oil. Then pour in the caramel mass about 1 1/2 cm thick, smooth it down and let it cool down.
While still lukewarm, cut into 2x2 cm cubes with a sharp knife. Leave to cool completely. Remove from the tin and give away in tins or individually wrapped in cellophane paper.