For the pudding: Bring the dates and milk to a simmer in a small saucepan over medium heat, and simmer until the dates begin to soften, 3 to 4 minutes. Remove from the heat, and stir in the baking soda (it will foam a bit); set aside to cool slightly.
Whisk together the flour, baking powder, salt and pumpkin pie spice in a medium bowl until combined; set aside.
Whisk together the sugar, butter, eggs and zest in a large bowl until smooth. Whisk in the date mixture until just combined. Stir in the flour mixture until just combined.
Line the insert of a 6-quart slow cooker with a double layer of aluminum foil, pressing it smoothly into the corners, and spray well with cooking spray. Pour the batter into the foil, and turn the cooker on low for 4 hours. Fold a double layer of paper towels, and place just under the lid across the pot to absorb the excess moisture and form a tight seal. Cover tightly with the lid. Cook until the middle of the cake has set and a toothpick inserted in the center comes out clean. Let cool slightly, 15 to 20 minutes.
For the sauce: While the pudding cools, bring the sugar, cream and butter to a boil in a small saucepan over medium-high heat; cook, stirring often, until smooth, about 5 minutes. Remove from the heat, and add the nutmeg.
To assemble: Poke holes in the cake with a skewer, and pour half the toffee sauce over it. Let the cake cool, 10 to 15 minutes. Serve with ice cream or whipped cream.
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