Place the dates and baking soda in a medium heat-proof bowl and pour 1 cup boiling water over them, making sure they are all submerged in water. Let them sit for 1 hour. Puree dates and soaking liquid in a food processor or blender. Another option: pulse them in a food processor until the mixture is combined but still has texture (if you want a little texture to your cake. This is more traditional.) Set aside.
Preheat the oven to 350 F degrees.
Grease a 9-inch springform pan with butter and line the bottom with unbleached parchment paper. You can also do this in an 11 x 7-inch pan and cook for a little less time or an 8 x 8.
Sift the flour and baking powder over a large bowl. Stir in the salt.
In a stand mixer fitted with the paddle attachment, cream the butter and sugars at medium-high speed until light and fluffy, 4-5 minutes. Add the eggs and beat until well combined. Beat in the vanilla. Add the date puree and flour mixture, alternating each one, to the butter mixture, and combine well.
Pour the batter into the prepared pan and smooth the top with a spatula. Bake in the center of the oven for 35-45 minutes (35 minutes is perfect in my oven), until the cake is beautifully golden brown, and top is starting to set and feel springy. Do not cook to the point that the cake is firm.
Immediately after removing the cake from the oven, EITHER poke several holes in the cake with a thin skewer and pour 1⁄2 cup of toffee sauce over the top OR do not poke with a skewer and just pour 1⁄2 cup sauce over the top of the cake. Let the cake rest for at least 15 minutes before serving. Slice warm cake with the rest of the warm toffee sauce on the side.
Serve with additional accompaniments, if desired. If you want to make the cake ahead, still pour sauce over immediately, but stick it under the broiler for a minute or two to warm the top of the cake. Do not let the toffee topping burn though.