Make the cake: Heat the oven to 350°F. Butter a 11x7-inch nonstick baking pan that’s at least 1 inch deep. If your pan isn’t nonstick, butter the sides and then line it with enough parchment to come 1 inch up the short sides; butter the parchment as well.
Put the dates in a small saucepan with 1 cup water and bring to a boil over high heat. Reduce the heat to medium and simmer until softened, about 5 minutes. Remove from the heat, stir in the baking soda, and set aside. (The mixture will foam up and take on a greenish color; this is normal.)
Combine the butter and the golden sugar in a bowl. Beat with a hand mixer on high speed until the mixture is well combined and lighter in color, about 4 minutes. Beat in the vanilla. Add the eggs one at a time, beating well after each addition. With a wooden spoon, stir in the flour and then stir in the date mixture; the batter will be sloppy. Pour the batter into the greased pan and bake until it's risen, a deep golden brown, and firm to the touch but still a bit spongy (it should spring back a little, but not entirely, when indented, 35 to 40 minutes.
Meanwhile, make the sauce:
Put the muscovado sugar, honey and butter in a small saucepan and heat gently, stirring until the sugar dissolves. Bring to a simmer and cook until it gets thick and bubbly, 2 to 3 minutes. Stir in the cream, let it bubble down and then remove the pan from the heat.
When the cake is done, remove it from the oven and let it rest for 5 minutes; then turn it out onto a cutting board and invert it onto a wire rack to cool slightly. Cut the warm cake into slices or squares, put on serving plates along with a scoop of ice cream, if using, and drench with the sauce.