Preheat the oven to 350°F (175°C).

Butter an 8-by-12-inch glass baking dish.

In a medium heatproof bowl, combine chopped dates and cinnamon sticks.

Pour boiling water over the dates and cinnamon sticks.

Let stand for 30 minutes.

Drain the dates in a colander, discarding the cinnamon sticks.

In a large bowl, cream together softened butter, brown sugar, and vanilla seeds using an electric mixer until fluffy.

Beat in the eggs, one at a time, scraping down the side of the bowl after each addition.

In a medium bowl, whisk together flour and baking soda.

Gradually add the dry ingredients to the butter mixture, mixing at low speed until just combined.

Stir in the drained chopped dates.

Pour the batter into the prepared baking dish.

Bake for 45 minutes, or until a toothpick inserted into the center comes out clean.

While the cake is baking, prepare the toffee sauce.

In a medium saucepan, bring heavy cream and brown sugar to a boil.

Add the butter and stir over moderate heat until melted and smooth.

Keep the toffee sauce warm.

Once the cake is out of the oven, poke holes all over the top with a fork.

Drizzle 2 cups of the hot toffee sauce over the cake.

Return the cake to the oven and bake for 5 minutes longer, until the toffee sauce is bubbling but not fully absorbed.

Let the cake cool until most of the sauce has been absorbed, about 1 hour, poking additional holes periodically.

Cut the cake into squares.

Serve warm with sweetened whipped cream and remaining toffee sauce on the side.