Preheat the oven to 325 degrees F.
Using the extra butter, grease an 8-inch square baking pan, then using the extra flour, lightly dust the greased pan.
In a large bowl, add the chopped dates and the boiling water and allow the dates to sit, undisturbed, until they have swelled and softened, about 20 minutes.
Add the vanilla to the dates and stir lightly to combine.
Allow the dates to sit undisturbed.
Sift 3/4 cup of the remaining self-rising flour and the baking soda into a large mixing bowl.
In a separate bowl, add 6 tablespoons of the remaining butter and the cane sugar and using an electric handheld mixer on medium speed, beat until creamy and combined.
Gradually, add the beaten eggs, 1 at a time, to the butter mixture and beat well after each addition.
Add 2 tablespoons of the molasses to the egg mixture and beat well to combine.
Add 1/3 of the flour mixture to the egg mixture and fold to combine.
Add 1/3 of the milk to the egg mixture and stir to combine.
Add 1/2 of the remaining flour mixture and 1/2 of the remaining milk to the egg mixture, alternating between the two and folding between additions. Then, add the remaining flour mixture and the remaining milk, alternating between the two and folding between additions.
Add the soaked dates and any liquid in the bowl to the batter and stir gently to combine.
Pour the batter into the prepared baking pan.
Bake in the center of the oven until it is raised and firm to the touch, about 45-50 minutes.
Transfer from the oven and allow it to cool in the pan for 5-10 minutes.
Turn the pudding out onto a serving plate.
In a saucepan over medium heat, add the muscovado sugar, the remaining 4 tablespoons of the butter, and 1/2 cup of the heavy cream and stir to combine.
Cook the butter mixture until the butter is completely melted.
Increase the heat to medium-high and bring the butter mixture to a boil.
Boil the butter mixture, while stirring constantly, until the sugar has completely dissolved.
Add the remaining molasses to the sauce mixture and stir to combine.
Allow the sauce to bubble until thickened, about 2 minutes.
Transfer the sauce from the heat and allow it to cool for 1 minute.
Add the remaining heavy cream to the sauce and stir to combine.
Drizzle the pudding with the sauce.
Serve.