Preheat your oven to 400 degrees F. If you're using dark metal pans, it’s a good idea to reduce this to 375 to 385 degrees or adjust your baking time accordingly.
In the bowl of a stand mixer, combine the chocolate cake mixes, eggs, and oil. Beat on medium until everything is well combined. The dough should come together quickly and pull away from the sides of the bowl, indicating it’s ready.
Roll the dough into 1-inch balls and place them 2 inches apart on a lightly greased baking sheet or parchment paper. Bake for 7 to 8 minutes, until the cookies are slightly puffed, and the tops look dry and set. Don’t worry if they sink as they cool; that’s normal!
Once baked, remove from the oven and set aside to cool completely. During this time, prepare your frosting.
In a small bowl, melt together the white chocolate and milk in the microwave in 30-second intervals on low heat. Stir until smooth and set aside to cool to room temperature.
In a clean bowl, combine the strawberry puree, butter, and vanilla. Beat until smooth, then add the melted chocolate and mix until well combined.
Gradually add the powdered icing sugar, one cup at a time, and mix on low until combined. If you want a pop of color, add a bit of red or pink gel food coloring at this stage. Beat on high for 2-3 minutes until the frosting is light and fluffy.
For the ganache, combine the chocolate and milk in a small pot over low heat. Stir continually until the mixture is smooth and combined. Allow it to cool until it thickens to a spreadable consistency.
Line two baking sheets with plastic wrap. Place half of the cookies on each sheet, with the bottom facing up. Spread or pipe frosting on all the cookies on one sheet and set them in the fridge to help the frosting set.
On the other sheet, spread the ganache on all the cookies. When the frosting is set, remove it from the fridge and sandwich together one cookie from each sheet.
If desired, roll the cookies in sprinkles or non-pareils for an extra festive touch. Store them in the fridge for the frosting to stay firm, although they freeze well, too!
