The rain is coming down this Monday morning. This recipe for Rainbow Chip Sheet Cake was already on the docket, but now that I’ve looked out the window, I hope the bright cake will bode as well for the weather later (a rainbow, followed by sunshine?!?!) as it will for all the future birthdays at which sugar coma-inducing slices will delight partygoers and party-givers alike.

This cake is part of neither my sweets-eating nor sweets-baking history, but I’d venture a guess that some of you grew up with rainbow chip cake and icing (that or Funfetti). Rainbow chip cake mix prevails, but the frosting got axed last year, to great sadness ^[1] among the rainbow chip-loving set, which includes my friend Kenny-at whose 2013 party I first witnessed true love for rainbow chips, but whose 2014 Prospect Park birthday picnic was threatening to be disastrous, thanks to the discontinuation of the sprinkle-spangled icing from a can.

Anika (Kenny’s girlfriend) to the rescue. She found a source of rainbow chips, and I volunteered to make the cake. I used my trusty yellow cake recipe, which is flavored with lemon zest, and baked the batter in a sheet pan. (I find sheet cakes particularly accessible, and they save time. Plus, when you cut squares, you end up with cupcake-like proportions of icing to cake, which I love.)

I stirred together a classic cream cheese icing, adding extra sweetener to mock the stuff that comes in a can, then poured in the rainbow chips. I piled the icing on top, then set the whole cake on my slate board ^[2] and carried it (biceps burning) to the park. When we’d eaten all of Anika’s grilled green chili turkey burgers and tasty guacamole, we finally brought out the cake. As the birthday guys blew out the candles ^[3], I was suddenly kind of worried. Would the cake meet Kenny’s expectations?

Fortunately, all the guests ate plenty of cake. Kenny led the way in doling out extra icing from a container I’d brought when the whole bowl I’d mixed up didn’t fit on top of the cake. This was success. Sweet success.

**Recipe**

Rainbow Chip Sheet Cake
Serves at least 12
Hat tip to this post ^[4] for pointing me to Wilton’s rainbow chips on Amazon

Here’s the thing to know about the Wilton rainbow chips: they actually have chocolate (or a chocolate-ish substance) beneath the colorful coating-like tiny little M&Ms. So, I don’t recommend throwing them into the cake unless you want smears of melty chocolate to mar your rainbow. If you want to go even more DIY, Ashley at Not Without Salt posted a how-to on making rainbow chips from scratch ^[5].

Ingredients
For the cake:
4 large eggs, at room temperature
1 1/3 cups sour cream, divided
2 teaspoons vanilla extract
Zest of 2 lemons
3 1/2 cups all-purpose flour
2 cups sugar
1 teaspoon baking powder
1 teaspoon baking soda
1 teaspoon salt
20 tablespoons (2 1/2 sticks) unsalted butter, at soft room temperature

For the icing:
12 ounces cream cheese (usually 1 1/2 packages)
2 sticks butter (8 ounces, 16 tablespoons), softened
1 1/2 cups confectioners sugar
2 tablespoons honey
1 teaspoon vanilla extract
1 1/2 5.25 ounce jars Rainbow Chip Crunch ^[6]

First, make the cake: Preheat the oven to 350°F. Butter a 9-by-13 inch rectangular cake pan with high sides. Cut out some parchment to line the bottom and short sides, then grease that with softened butter too.

Whisk the eggs with 6 tablespoons of the sour cream, vanilla, and lemon zest.

In a separate bowl–the bowl of a stand mixer if you have one–whisk together the flour, sugar, baking powder, soda, and salt. Add the butter, cut into rough tablespoon-sized chunks, and the remaining sour cream, and, using your hand-held mixer or your very strong arm if you don’t have a stand mixer, beat this together for nearly two minutes. It will be very creamy. Pour in the egg mixture in two parts, beating for nearly a minute after each.

Pour the batter into the cake pan and bake for 30 to 40 minutes, until the edges are golden and pulling away from the sides of the pan. A toothpick inserted will come out clean, and the cake will bounce back when you press it lightly. Run a butter knife along the edges, then remove the sides of the pan and cool completely. When cool, flip the cake to remove the parchment from the bottom.

To make the icing: combine all the ingredients in the bowl of an electric or handheld mixer. (You can also use a food processor, just transfer to a bowl to fold in the rainbow chips.) Either way, blend until very smooth. Taste, adding more sugar or cream cheese/butter to get the taste and consistency you like. Stir in the rainbow chips. You can make this ahead of time; refrigerate until 2 hours before you need to use, then set on the counter to come to room temperature.