Preheat the oven to 180 °C. Butter a 65 cm x 30 cm oven pan generously and line the bottom with wax paper.
For the truffles, beat the sugar, eggs and jam together in a stand mixer on medium speed until pale and fluffy. Sift in the flour, salt and bicarbonate of soda and mix well. Melt the butter in the milk. Add the vinegar and vanilla to the egg mixture and slowly add the butter and milk to the batter. Mix until completely blended.
Pour the batter into the prepared pan and bake for 20–25 minutes until the pudding begins to pull away from the sides of the dish and a toothpick inserted in the centre of the pudding comes out clean.
Combine the sauce ingredients in a saucepan and heat only long enough to melt the butter. Pour the sauce over the pudding as soon as it comes out of the oven, and allow it to be absorbed. Let the pudding rest and cool down, then refrigerate for at least 1 hour.
Scoop out a full teaspoon of the pudding and place in the palm of your hand. Roll gently into a ball. Skewer the ball onto a sprig of rosemary and dip into the melted chocolate, then place on a drip tray to harden. If you want to be fancy, use a blowtorch and smoke the rosemary right before serving or in front of your guests as we do at JAN.
Recipe by Shades of Cinnamon at https://www.shadesofcinnamon.com/jan-a-breath-of-french-air/