In a 3- to 4-quart pan, combine dates and 1 1/2 cups water. Bring to a boil over high heat and stir often until most of the liquid is absorbed, 5 to 7 minutes; watch carefully as liquid reduces to avoid scorching. Let cool at least 15 minutes.
Butter and flour a 9-inch square pan. In a bowl, mix 1 1/2 cups flour with baking powder and baking soda.
In a food processor, whirl cooked dates until smooth. Add 1/2 cup butter, sugar, eggs, and flour mixture; whirl until well blended. Scrape batter into pan and spread level.
Bake in a 325° oven until cake springs back when lightly pressed in the center and edges begin to pull from pan sides, 30 to 40 minutes. Let cool in pan at least 5 minutes. Invert onto a rack. Cut warm or cool cake in half horizontally.
Rinse and dry baking pan. Pour about 1/2 cup hot sticky sauce into pan. Lay cake bottom, cut side up, in pan. Pour about 2 cups hot sticky sauce evenly over cake. Lay cake top, cut side down, in pan. Pour remaining hot sticky sauce evenly over it. Let stand at least 30 minutes or up to 1 hour. Invert a flat, rimmed plate over pan; holding containers together, turn over, and lift pan off cake. Cut into rectangles and transfer with a spatula to plates. Add crème fraîche to taste.
Sticky sauce. In a 5- to 6-quart pan over high heat, boil 1 1/2 cups whipping cream, 1 1/2 cups sugar, 1/4 cup (1/8 lb.) butter or margarine, and 1/4 cup light corn syrup, stirring frequently, until golden brown, 6 to 8 minutes. Remove from heat and immediately stir another 1 1/2 cups whipping cream into pan. Return to high heat and stir until sauce comes to a rolling boil, 1 to 2 minutes. Use hot, or let cool, cover, and chill up to 2 days; stir over high heat until hot. Makes 3 1/2 cups.