Preheat oven to 350 degrees. Spray pan (either 8 x 11" or 9 x 9" pan) with non-stick cooking spray.
Combine the cake mix, oil, and egg in a large bowl.
Add the milk to the bowl slowly, you want the batter to remain as dense as possible.
Fold in the strawberry jam and white chocolate chips.
Dump batter in prepared pan and spread to the edges.
Bake for 25-30 minutes (they will be a little soft/gooey in the middle- just let them sit for about 20-30 minutes and they will set up).
To make frosting, combine all frosting ingredients together in a bowl and frost bars when cool. (frosting is optional because these taste amazing without frosting, but I am a serious frosting lover, so I added some and loved the way it turned out).
Notes
Add milk slowly to keep batter dense
Let cake cool completely before frosting
Don't overbake, the bars may seem gooey but will set up