Preheat the oven to 350°F. Butter a 10-by-14-inch glass or metal baking dish or pan.

In a small bowl, combine the dates and baking soda. Pour the hot water over the dates and mix with a fork until they have mostly dissolved and are pulpy, about 5 minutes.

Scrape the seeds from the vanilla bean into a large bowl. Whisk in the granulated sugar, egg, and egg yolk until the mixture is pale yellow and falls in smooth ribbons when lifted with a spoon. Stir in the date mixture, incorporating it completely.

In a small bowl, sift together the flour and baking powder. Gently fold the flour into the date mixture until just incorporated.

Pour the batter into the prepared baking dish and bake until a skewer inserted in the center comes out clean, 35 to 40 minutes. Leave the cake in the pan for about 40 minutes before serving.

To make the whiskey sauce: In a large, heavy-bottomed saucepan, melt the butter with the brown sugar. As soon as the sugar has dissolved, gradually add the cream, pouring in a steady stream while whisking constantly. Remove from the heat and whisk in the whiskey.

Pierce the cake all over twelve to twenty times with a butter knife or a skewer. Pour half of the sauce over the top of the cake, guiding it into these holes, and set aside the rest.

Cut the cake into squares and drizzle with the remaining whiskey sauce. Serve on dessert plates, accompanied by scoops of gelato.