Bring dates and 1 ¼ cups water to a boil in a medium heavy saucepan with tall sides. Remove from heat; stir in baking soda (mixture will become foamy). Set aside; let cool.
Puree the dates and water in a food processor or blender.
Using a stand mixer or hand mixer, beat butter, sugar, and vanilla in to blend.
Whisk flour and baking powder together in a small bowl.
Crack the eggs into a jug or cup for easy pouring. Alternate between adding the eggs one at a time into the stand mixer, adding a half of the dry mix, and a half the pureed simmered date mixture, mixing between each addition, until everything is added and combined, repeat procedure with the second half of mixing.
Pour batter into a buttered square casserole, going no more than halfway up the sides.
Bake until a tester inserted into center of pudding comes out clean, 45-60 minutes. Let cool for 30 minutes.
Make the toffee sauce while the pudding is baking. (recipe follows)
Poke all over with a fork and then pour rum all over so that it absorbs into the pudding.
Pour the toffee sauce all over and allow it to absorb, then pop the pudding back into the oven for 20-30 minutes or until the toffee sauce starts bubbling around the edges.
Combine the sugar, cream, and butter in a high sided saucepan and bring to a boil over medium heat.