Heat the oven to 350°F (175°C). Butter a 10-inch round or square baking dish, and set it aside.

Sift together the flour and baking powder in a bowl.

Place the chopped dates in a bowl, pour the boiling water over them, and stir in the baking soda. Let the dates stand while you prepare the batter.

In a large bowl, beat the softened butter and granulated sugar together until light and fluffy, about 2 minutes.

Beat in the egg and vanilla.

Mix in the sifted flour mixture and then fold in the date mixture with all of its liquid.

Pour the batter into the prepared dish and bake for about 35 minutes, or until the cake is set.

While the cake bakes, make the toffee sauce by combining the butter, heavy cream, and brown sugar in a heavy saucepan. Bring to a boil while stirring, then cook gently over medium-low heat for about 8 minutes.

Spoon about 1/3 cup of the warm sauce over the baked cake and spread it out evenly.

Broil for about 1 minute, just until bubbling. Watch closely to avoid burning.

Cut the cake into squares, spoon into bowls, and top with extra warm toffee sauce and softly whipped cream.