Makes three 6-inch cakes or two 8-inch cakes

There’s something so beautifully simple and sophisticated when
it comes to berries on cakes. They speak volumes with their
gorgeous ruby reds, deep purples, and dark blues. Blackberries
make such a stunning buttercream, naturally tinting the cake
with soft purple hues without having to use any artificial
coloring. I left the seeds in my buttercream, but you can always
strain them out. I wanted to pair something zesty with this
simple blackberry cake, and lime curd was definitely the way to
go. It’s easy to make and adds just a bit of texture difference to
the rest of the cake. Lime curd is naturally a bit of a light tan
color, so I added a touch of food coloring to give it that soft
green color, echoing more of a lime vibe. Don’t add too much
though, or you’ll be singing the Ghostbusters theme with
radioactive slime oozing between the layers. Hope you enjoy
this one as much as we did!


  • 1 cup buttermilk
  • 4 egg whites
  • 1 Tbsp. Mexican vanilla
  • ½ cup sour cream
  • ⅓ cup vegetable oil
  • zest from 3 limes (about 3 Tbsp.)
  • juice from 1 lime
  • 1 box Duncan Hines white cake mix


  • 3 whole eggs
  • ¾ cup sugar
  • pinch of salt
  • ½ cup lime juice
  • zest of 1–2 limes
  • 4 Tbsp. unsalted butter, cubed
  • green gel food coloring


  • 1½ cups (3 sticks) unsalted butter
  • pinch of salt
  • ½ cup fresh blackberries, pureed (strain seeds if desired)
  • 1 tsp. raspberry or strawberry emulsion
  • 1 Tbsp. vanilla
  • ⅛ cup heavy cream
  • 6–7 cups powdered sugar, sifted


  • fresh whole blackberries

Lime Cake

  1. Preheat oven to 325 degrees. Prep three 6-inch cake rounds
    with a swipe of shortening and dust of flour. Set aside.
  2. In a medium bowl, whisk together the buttermilk, egg
    whites, vanilla, sour cream, oil, lime zest, and lime juice.
    Whisk until just combined. Sift in cake mix. Split cake batter
    between the three prepped cake rounds.
  3. Bake for 26–28 minutes until center is baked through—
    don’t overbake! Remove from oven, let cool in pan for 5
    minutes, then flip out onto a wire rack to cool until room

Lime Curd

  1. In a small bowl, whisk together the eggs, sugar, salt, and
    lime juice, and zest until thoroughly combined.
  2. Pour mixture into a small saucepan over low heat. Whisk
    steadily for about 5–10 minutes until it thickens. Don’t turn
    up the heat or the eggs will scramble. The curd is ready
    when it coats the back of a spoon without being translucent.
  3. Remove curd from the heat, then add in the butter cubes.
    Stir to combine. Mixture will be a bit thin. Add in a very tiny
    bit (I’m talking a toothpick prick) of green coloring. It should
    be a very pale green. Place a piece of plastic wrap over the
    top of the curd and store in the fridge until it reaches room
    temperature (colder, even) and thickens.

Blackberry Buttercream

  1. In a stand mixer fitted with a paddle attachment, whip
    butter for about a minute until light and fluffy. Scrape down
    the sides of the bowl.
  2. Add in salt, blackberry puree, emulsion, vanilla, and heavy
    cream until combined.
  3. Slowly add in powdered sugar, about a half cup at a time.
    Add in more heavy cream if needed for a thinner
  4. Whip on high for a minute to create a soft buttercream,
    then back down to low for 30 seconds to beat out any air


  1. On a cake turntable, tape a 6-inch cardboard round on top
    of an 8-inch cardboard round. Top with a small amount of
    buttercream and spread it around to act like “glue” for
    holding the cake onto the board.
  2. Place on first cake round, add on about a cup of
    buttercream, spread it flat with an offset cake spatula. Pipe
    a dam around the outer rim, then spoon on about ¼ cup of
    lime curd. Add on next layer of cake and repeat with
    remaining two layers.
  3. Carefully crumb coat the cake and immediately place in the
    fridge to set for about 10 minutes, then add on the rest of
    the buttercream for the final coat, using a cake scraper for
    sharp edges. The lime curd is a very soft filling, so less is
    more. You can always add a dowel if it’s too slippery.
  4. Place fresh blackberries in a crown on the top rim of the
    cake. Serve with extra lime curd.