Preheat the oven to 350°F (175°C). Butter and lightly flour a 9x9-inch (or similar) baking dish and set aside.
In a large bowl, cream together the Unsalted Butter and Granulated Sugar until light and fluffy. Beat in the Eggs one at a time, then stir in the Apricot Jam until well combined.
Sift together the All-Purpose Flour, Baking Soda and Salt in a separate bowl.
Make a quick buttermilk by mixing the Milk with the White Vinegar in a small jug and let it sit for 5 minutes.
Fold the dry ingredients into the butter-egg mixture in two additions, alternating with the buttermilk, mixing gently until just combined. Scrape the batter into the prepared dish and smooth the top.
Bake for about 30–40 minutes, or until the top is deep golden and a skewer inserted into the center comes out clean.
While the pudding bakes, make the sauce: in a saucepan over medium heat combine the remaining granulated sugar, Water, the leftover butter from earlier, and a pinch of salt; heat until the sugar dissolves. Stir in the Heavy Cream and simmer briefly until the sauce is smooth, then remove from the heat and stir in the Vanilla Extract.
When the pudding comes out of the oven, immediately pierce the surface all over with a skewer or fork and pour the hot sauce evenly over the pudding so it soaks in. Let rest for 10–15 minutes before serving warm, ideally with extra cream or ice cream.
