Preheat oven to 350 degrees . Grease an 8-inch, parchment-lined springform pan. In a saucepan, bring 3/4 cup water and the dates to a simmer, covered. Remove from the heat; let cool.
In a medium bowl, whisk the flour, baking powder, baking soda and 1/2 tsp. salt. Using an electric mixer, beat the brown sugar and 6 tbsp. butter on high until fluffy, scraping down the bowl. Beat in the eggs 1 at a time. On low speed, mix in half of the flour mixture. Mix in the date mixture, milk, vanilla and remaining flour mixture. Scrape into the pan, smoothing the top. Bake until the top is springy, about 50 minutes.
In a small, heavy saucepan, bring 1 cup granulated sugar and 3 tbsp. cold water to a boil without disturbing. Boil until the mixture begins to turn amber, about 5 minutes. Swirl the pot and when the color is deep amber, remove from the heat. Stir in the remaining 2 tbsp. butter, then 2/3 cup cream; stir over low heat until smooth. Stir in the remaining 1/4 tsp. salt.
Let the cake cool on a rack for 5 minutes. Using a skewer, poke deep holes into the cake at 1-inch intervals. Spoon about half of the caramel onto the warm cake, swirling with the back of the spoon. Let the cake cool completely in the pan, then cover and let stand at room temperature for 12 to 48 hours.
When ready to serve, preheat the oven to 325 degrees . Reheat the cake for 15 minutes. In a bowl, whip the remaining 1 cup cream and 1 tbsp. granulated sugar. Rewarm the caramel sauce. Serve the cake warm with the whipped cream and sauce.