Preheat an oven to 350°F (180°C). Lightly grease a 9-inch (23-cm) square baking pan.
To make the crust, in the bowl of an electric mixer fitted with the flat beater, combine the crust mix, egg and butter. Beat on low speed until the ingredients are well combined, 1 to 2 minutes. Transfer the mixture to the prepared pan and press firmly into the bottom.
To make the filling, in the clean bowl of an electric mixer fitted with the flat beater, beat the cream cheese, eggs and butter on low speed until well combined, 2 to 3 minutes. Add the filling mix and beat on medium-low speed until completely incorporated, about 2 minutes. With the mixer on medium-low speed, add 1/4 cup (60ml) water and beat until well combined, about 1 minute more.
Spread the filling evenly over the crust. Bake until the edges of the filling are set but the center still jiggles slightly, 25 to 35 minutes. Transfer the pan to a wire rack and let cool for at least 20 minutes. Cut into squares and serve.
Makes sixteen 2 1/4-inch (6-cm) bars.
For thicker bars, use an 8-inch (20-cm) square pan and increase the baking time by 5 to 10 minutes.

Williams Sonoma Gooey Pumpkin Bar Baking Mix