Topping:
1 cup sour cream
1/4 c packed light brown sugar
1. Preheat oven 325ºF. Lightly grease 13x9 baking pan.
2. Set aside 1/2 cup cake mix.
3. Place remaining mix, melted butter, and 1 egg in large mixing bowl. Blend with mixer on low for 2 minutes. Scrape down the sides. The batter should come together in a ball. With your fingertips, pat the batter evenly over the bottom and up the sides of the pan, smoothing the top.
4. For the filling, place the cream cheese and the sweetened condensed milk in the same mixing bowl that was used to make the crust, and with the same beaters (no need to clean either) blend on low speed until just combined, about 30 seconds. Add the reserved cake mix. the remaining 3 eggs, the pumpkin, brown sugar, cinnamon, nutmeg, and ginger and beat on medium speed for 1 minute. Pour the filling onto the crust and spread so that it covers the entire surface and reaches the sides.
5. Bake the cheesecake until it looks shiny and the center no longer jiggles when you shake the pan, 40 to 45 minutes. Remove the pan from the oven and prepare the topping. (Leave the oven on)
6. For the topping, place the sour cream and brown sugar in a small mixing bowl and stir until well combined. POur the topping over the cheesecake, and return the pan to the oven.
7. Bake until the topping sets, 7 to 10 minutes. Remove the pan from the oven and place it on a wire rack to cool, 30 minutes. Lightly cover the pan with plastic wrap and place the pan in the refrigerator to chill for at least 1 hour, but preferably 24 hours for the flavors to meld. Cut into squares and serve.
Store this cake, covered in plastic wrap or aluminum foil, in the refrigerator for up to 1 week. Or freeze it, wrapped in foil, for up to 2 months. Thaw the cake overnight in the refrigerator before serving.
