Preheat the oven to 160°C fan and spread butter over a medium sized baking dish.
Cover the potatoes in the tea and baking soda for 10 minutes, then remove the tea bag and mash it all up.
Beat together the butter, all the sugar and molasses, then add the eggs, flour, baking soda, vanilla and salt. Mix in the mashed potatoes.
Pour into the dish and bake for 30–40 minutes.
For the sauce, melt the butter, all the sugar and treacle until smooth, then add the cream and simmer until it thickens. Add the salt and pecans.
For the maple cream, whip the cream to soft peaks. Add 2–3 tablespoons of maple syrup and drops of vanilla, then fold gently to combine.
Pierce the warm sponge with a skewer and pour half the sauce over it. Serve the portions with more sauce and a spoonful of the whipped maple cream, or with ice cream or custard.