1. Preheat oven to 350°.
2. To prepare cake, combine first 5 ingredients in a small saucepan; bring to a boil, stirring occasionally. Remove from heat, and let stand 10 minutes or until dates are tender.
3. Weigh or lightly spoon flour into dry measuring cups; level with a knife. Combine flour, baking powder, and 1/2 teaspoon salt in a bowl. Stir in date mixture, granulated sugar, vanilla, and egg until well combined. Pour batter into a 9-inch springform pan coated with cooking spray. Bake at 350° for 20 minutes.
4. To prepare topping, combine brown sugar and remaining ingredients in a small saucepan; bring to a boil. Reduce heat, and simmer 1 minute. Pour brown sugar mixture over cake; bake at 350° for an additional 13 minutes or until a wooden pick inserted in center comes out clean. Cool in pan 5 minutes on a wire rack. Run a knife around outside edge. Cool completely on a wire rack.
Prepare the topping while the cake bakes in step 3.