In the bowl of an electric mixer, cream the 6 oz. of butter with the sugar.
Add the eggs, one at a time. Scrape down the sides of the bowl as necessary.
Whisk together the flour, baking powder, and salt. Add the dry ingredients to the mixer bowl and mix on low until you have a thick batter. Scrape down the sides of the bowl and beat the mixture one last time.
Transfer the mixture to a container, seal, and refrigerate overnight.
Buttered rum sauce preparation:
In a large saucepan, pour the maple syrup, cream, and the rum. Add a generous pinch of salt.
Add the butter, and stir the mixture on medium heat until the butter is melted.
Bring the sauce to a simmer, and continue simmering on low for at least 5 minutes. Stir often, you don’t want the sauce to scorch on the bottom.
Remove the sauce from the heat and set aside.
Assembly of the puddings:
Preheat the oven to 450°F (230 °C).
In each of the large ramekins or oven-proof soup dishes, place a scoop of cake batter.
Poor the sauce around the dollop, at least until half way up the dish, but no more than three-quarters full (the more sauce you add at this stage, the more you will have left after baking!). Store any remaining sauce for later (for buttered rum ice cream sundays perhaps…)
Place all the filled ramekins on a rimmed baking sheet to catch the drips (the drippings on the pan may burn, this is normal).
Bake in the preheated oven for 20–30 minutes (a cake tester should come out clean).
Let cool at least 5 minutes before serving (or else you risk a seriously scorched tongue!).