Step 1

Heat the oven to 350°F. Grease a 9-inch square baking dish.

Step 2

Prep the cake: Measure out 1⁄2 cup of the cake mix and set aside for the topping. Combine the remaining cake mix, the sour cream, and egg in a medium bowl and beat until just smooth, with no lumps remaining.

Step 3

If you are using canned or frozen fruit, mix it into the batter and pour the mixture into the prepared pan. If you are using fruit filling, pour half the batter into the prepared pan, cover with the fruit filling, and top with the remaining batter.

Step 4

Prep the topping: Toss the reserved 1⁄2 cup cake mix with the cinnamon and butter in a small bowl until the mixture is crumbly and streusel-like. Sprinkle it evenly over the cake batter.

Step 5

Bake for 50 to 60 minutes, until the top is golden brown and a thin knife plunged into the center comes out clean or with a few traces of fruit filling. Cool completely in the pan before cutting into 2-inch squares and serving.

Step 6

Cover leftovers with plastic and refrigerate for up to 1 week. If you have time, throw slices in the toaster oven to make something exciting and new for breakfast