• Preheat the oven to 350°F. Finely chop the pitted dates and place them in a heatproof bowl. Add the baking soda and ½ teaspoon vanilla extract. Pour the boiling water over the dates and stir. Let stand for 15 to 20 minutes. Do not drain.
  
• While the dates soak, cream the softened butter, dark brown sugar, granulated sugar, and molasses together in a mixing bowl. Add the eggs one at a time, mixing after each addition.
  
• In a separate bowl, stir together the flour, baking powder, and salt. Gradually add to the butter mixture, mixing on low speed just until combined.
  
• Mash the dates and their soaking liquid with a fork until jam-like, or puree the mixture in a food processor. Mix the entire date mixture into the batter until combined.
  
• Grease a 2-quart casserole dish or an 8-inch square baking dish. Spread the batter in the prepared dish.
  
• Bake for 30 to 35 minutes, or until a toothpick inserted into the center comes out clean.
  

Sticky Toffee Sauce:

• While the cake bakes, make the sauce. Combine the brown sugar and butter in a heavy saucepan. Bring to a gentle simmer, whisking constantly until combined. Carefully stir in the heavy cream and return to a simmer. Simmer for 5 to 6 minutes, until slightly thickened. Remove from the heat and stir in the salt and vanilla.
  
• Use the small end of a chopstick or a small dowel to poke holes over the warm cake, going only about halfway through. Spoon half the warm toffee sauce over the cake and allow it to soak in.
  
• Serve warm with vanilla ice cream or whipped cream, if desired, and spoon the remaining sauce over each serving.