Preheat oven to 350 degrees.
Spray a 10-inch round or square baking dish, or extra large 6-cup muffin tin or ramekins with cooking spray; set aside.
Sift flour, baking powder, and espresso powder onto a sheet of waxed paper.
Finely chop the dates. Place in a small bowl and add the boiling water and baking soda; stir and set aside.
In a large bowl, beat the butter and brown sugar with an electric mixer until light and fluffy.
Add the egg and vanilla; beat until blended.
Gradually beat in the flour mixture until the dry ingredients are incorporated.
With a rubber spatula, fold in the chopped dates until blended.
Pour into prepared baking dish.
Bake until the cake is set and firm on top, about 35 minutes.
Remove from the oven and allow to cool on a wire rack.
Melt the butter, in a heavy saucepan.
Add the brown sugar and heavy cream, and heat to boiling over medium-high heat, stirring constantly.
Boil gently over medium-low heat, stirring occasionally, until mixture is no longer grainy, about 2 to 3 minutes.
Right before serving:
Unmold cakes (if using tins) and spoon about 1/3 cup of toffee sauce over the entire cake, spread evenly. (Spoon individual amounts if using tins).
Place under broiler until the topping is bubbly, about 1 minute - do not burn.
Serve immediately with a scoop of ice cream and drizzled with additional warmed toffee sauce.