Preheat oven to 350. In a large bowl, mix together the cake mix, 1 cup of Dr Pepper, water, melted butter, and eggs. Mix on low speed with a hand mixer for 30 seconds until combined. On medium speed, mix for 2 minutes.
In prepared cupcake tins, fill each section with about 3 tablespoons of the cake mix. Bake for 14-19 minutes until a toothpick inserted into the center comes out clean. This will make 24 cupcakes. Let cool on a wire rack for 5 minutes, turn cupcakes out and let cool completely.
While the cupcakes are cooling make the buttercream frosting, or frosting of your choice.
To make the cupcake jars, cut each cupcake in half. Place one-half into the bottom of a pint-sized jar. Brush with a little bit of the remaining Dr Pepper. Top with a swirl of frosting. Add a sprinkle of chocolate chips. Repeat two more times.