Preheat oven to 350°F (175°C).
In a large bowl, combine cake mix, melted butter, milk, vanilla extract, and eggs. Beat until smooth.
Pour batter into a greased 9×13 inch baking pan and bake for 20-22 minutes, or until a toothpick inserted comes out clean.
While cake cools, prepare the filling. Cream together softened butter, salt, and vanilla extract until light and fluffy. Gradually add powdered sugar and beat until smooth. Add milk, 1 teaspoon at a time, until desired frosting consistency is reached.
Once the cake is cool, cut it into circles using a cookie cutter.
Spread a generous dollop of creme filling on half the cake circles. Top with the remaining cake circles to create little sandwiches.
Time for the zebra stripes! Melt your white chocolate according to package instructions (or see recipe notes). Carefully spread or drizzle melted white chocolate over the cake sandwiches.
Now for the magic! While the white chocolate is still wet, drizzle melted milk chocolate (or melted chocolate chips) to create zebra stripes.
Refrigerate cakes for at least 30 minutes to allow the chocolate to set
