How to Make It
Preheat the oven to 350°. Butter an 8-by-12-inch glass baking dish. In a medium heatproof bowl, cover the dates and cinnamon sticks with the boiling water and let stand for 30 minutes. Drain the dates in a colander and shake off any excess water; discard the cinnamon.
In a large bowl, using an electric mixer, beat the softened butter with the brown sugar and vanilla seeds until the mixture is fluffy. Beat in the eggs, one at a time, scraping down the side of the bowl after each addition. In a medium bowl, whisk the flour with the baking soda. Add the dry ingredients to the brown sugar mixture and beat at low speed until blended, then stir in the chopped dates. Scrape the batter into the prepared baking dish and bake for 45 minutes, or until the date cake is springy and a toothpick inserted in the center comes out clean.
In a medium saucepan, bring the heavy cream to a boil with the brown sugar. Add the butter and stir over moderate heat until melted; keep warm.
Using a fork, poke holes all over the top of the warm date cake. 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 around the edges but not fully absorbed. Let the cake cool until most of the sauce has been absorbed, about 1 hour, poking additional holes from time to time to help it absorb more sauce.
Cut the cake into squares and serve with whipped cream and the remaining toffee sauce on the side.