I knew I'd love Battenberg cake before I even tasted one because it's covered in one of my all-time favorite foods, marzipan! Marzipan is made of almonds and sugar and it has a dough-like consistency, sort of similar to fondant, so it's great for covering cakes. The Battenberg cake originated in England and is traditionally made in a checkerboard shape, with the cakes glued together by jam. There's no frosting on a Battenberg cake but the marzipan locks in loads of moisture and contributes such delightful sweetness and texture that you just don't miss it.
For the cake batter: Preheat the oven to 350 degrees F.
Turn an 8-inch square baking pan into a Battenberg pan: first, fold a long piece of foil onto itself a couple of times to a create a foil barrier to divide your pan in half, making sure that the barrier is at least the height of the pan or even a little more. Then, spray the pan and each side of the foil with cooking spray (to help the parchment stick) and line each half of the pan with two overlapping pieces of parchment paper, one going widthwise and one going lengthwise, with enough overhang to come all the way up the sides and then some. Get your scissors out and trim the parchment so that it lays nicely and doesn't curl around the corners and make you go crazy. Sorry, I know this is a lot of parchment paper (I reuse parchment all the time!). Okay, set this aside.
In a medium bowl, sift together the flour and baking powder, then lightly stir in the salt and set aside. In a large measuring cup, whisk together the heavy cream and sour cream and set aside.
In a stand mixer fitted with a paddle, cream together the butter, coconut oil and granulated sugar on medium-high speed until light and fluffy, 3 to 4 minutes. Add the eggs, one at a time, beating well after each and periodically scraping the sides of the bowl with a rubber spatula. Add the vanilla and mix to combine. Reduce the mixer to medium-low and add the dry mixture and cream mixture in 3 alternating additions, mixing until 80 percent combined.
Divide the mixture in half. In the first half, add a few drops of yellow food coloring and fold in the sprinkles as you mix until the batter is combined. Pour into one side of the pan and use a small offset spatula or a spoon to carefully spread it out evenly. In the second half of the batter, add a few drops of red food coloring and fold it in as you mix until the batter is combined.
Pour into the other side of the pan and use a small offset spatula or a spoon to carefully spread it out evenly. Bake until the tops of the cakes are browned and a toothpick inserted into the center comes out with a few crumbs on it; begin checking for doneness at 45 minutes. Let cool in the pans for 10 minutes, then use the parchment wings to lift them out of the pans and onto a wire rack to cool completely.
Level the cakes and trim off the sides if they're uneven. Halve each cake crosswise to yield 4 equal rectangles that are as wide as they are thick (measure the thickness of the cake once it's leveled, then turn your ruler 90 degrees to measure that same amount on top of the cake and score with an accordion pastry cutter). Enjoy a bite of cake scraps and set these aside.
To assemble: Knead the marzipan with the blue food coloring to get your desired color, dusting with powdered sugar if it gets too sticky. On a silicone mat (or a big piece of parchment or a counter dusted with powdered sugar, but I strongly recommend a silicone mat so that you don't get powdered sugar all over what will eventually become the outside surface of the marzipan), roll the marzipan out into a rectangle that's about 7 1/2 inches wide by 13 inches long, dusting the top with powdered sugar as needed to prevent sticking, and rolling in a scattering of sprinkles at the end. Trim the edges so they're straight. Brush all over with a thin layer of jam and place a rectangle of pink cake at one end. Brush the exposed surfaces with a thin layer of jam. Squish a rectangle of sprinkle cake right next to it and brush the exposed surfaces with a layer of jam. Stack the other two rectangles of cake on top, brushing with jam, to form a checkerboard pattern. Carefully roll it onto its side, pressing the marzipan all over so that it sticks, then continue to roll until the cake is covered. Trim off any excess marzipan, then decorate with additional marzipan decorations as desired.
Wrap in firmly plastic wrap and let set in the fridge for a couple of hours. Let come to room temperature and enjoy!