Preheat your oven to 375°F (190°C). Grease 6 individual 4-ounce ramekins with nonstick cooking spray and place them on a baking tray.
In a food processor, combine butter, baking soda, salt, both sugars, eggs, vanilla, and flour. Pulse until just combined. Add the prunes and hot water, then pulse again until the mixture is nearly smooth.
Spoon the mixture into the ramekins, filling each about two-thirds full. Bake for 18 minutes or until the tops are just firm and spring back when touched. Remove from the oven and let cool slightly.
Meanwhile, preheat the broiler, positioning the rack 4 inches from the heat source.
Prepare the toffee sauce by melting the butter in a medium saucepan over medium-high heat. Add cream, brown sugar, and a pinch of salt. Whisk continuously until the mixture starts to bubble. Reduce heat to medium-low and cook for another 3-4 minutes until the sauce thickens.
Carefully slice each pudding in half horizontally and place the bottom halves back in the ramekins. Drizzle a little toffee sauce over them, then top with the remaining pudding halves. Drizzle more toffee sauce on top.
Place the ramekins under the broiler for 1-2 minutes until the sauce is bubbly and sticky—watch closely to prevent burning.
Remove the puddings from the ramekins and serve on plates, drizzling with more toffee sauce. Optionally, top with whipped cream or a drizzle of heavy cream.