Gluten-free Coffee Walnut Cupcakes, with Mango Rum filling, and Salted Caramel Buttercream

When your oven gives up on you and you have to stay idle for days, while waiting for your new stove, your mind starts planning… flavors combinations, recipes, ingredients, and the creativity soars. Sometimes the results are not as we imagined,

These cupcakes batter were inspired by the British coffee walnut cake – I used buttermilk instead, and I apologize to purists for it. I also had some mango puree in my freezer – I buy Boiron purees when available, either on Amazon or at the Webstaurant Store, but you can puree fresh mango instead – and I wanted to spice it up with some rum for a filling. Lastly, I had used a wonderful salted caramel Swiss buttercream by Sweet + Savory for a cake that I had baked for a friend, and it was so good that I wanted to use it again, and share it with you.

The recipe requires a few steps, but they are all worth it, believe me! The salted caramel sauce for the buttercream is the same one I used to dress up my brownies, so if you have some leftover you can use it there. And I usually freeze any leftover buttercream up to two months. In addition, the mango rum curd can be used to fill any tart you like to bake in the next week or so – just keep it refrigerated until then.


Gluten-free Coffee Walnut Cupcakes, with Mango Rum filling, and Salted Caramel Buttercream

0 from 0 votes
Recipe by Simona Gluten-free, with contribution from Sweet + Savory blog and Nigella Dawson Course: DessertDifficulty: Medium
Prep time




Cooking time




  • For the mango rum curd
  • 240 g 240 mango puree 1 cup

  • 66 g 66 granulated sugar – 1/3 cup

  • 30 g 30 lemon juice – 2 Tablespoons

  • 10 g 10 cornstarch – 4 teaspoons

  • 3 large 3 yolks

  • 42 g 42 unsalted butter, 3 Tablespoons

  • pinch pinch salt

  • 1 Tablespoon 1 rum

  • For the salted caramel sauce
  • 150 g 150 granulated sugar – 3/4 cup

  • 180 g 180 heavy cream – 3/4 cup

  • 42 g 42 unsalted butter – 3 Tablespoons

  • 1/2 teaspoon 1/2 salt

  • For the caramel Swiss meringue buttercream
  • 6 large 6 egg whites

  • 300 g 300 granulated sugar – 1 1/2 cups

  • 1/2 teaspoon 1/2 salt

  • 340 g 340 unsalted butter, softened – 1 1/2 cups

  • 240 g 240 salted caramel sauce – 1 cup

  • For the coffee walnut cupcakes
  • 56 g 56 walnuts, chopped – 1/2 cup

  • 200 g 200 granulated sugar – 1 cup

  • 226 g 226 unsalted butter, softened – 1 cup

  • 212 g 212 Simona’s Flour Mix – 1 1/3 cups

  • 2 1/2 teaspoons 2 1/2 baking powder

  • 1/2 teaspoon 1/2 baking soda

  • 1/2 teaspoon 1/2 salt

  • 4 large 4 eggs

  • 90 g 90 buttermilk – 1/3 cup and 2 teaspoons

  • 4 teaspoons 4 espresso powder

  • 2 teaspoons 2 vanilla

  • 2 Tablespoons 2 glycerin


  • For the mango rum curd
  • In a medium saucepan bring the mango puree and the lemon juice to a boil. In the meanwhile in a medium bowl whisk the egg yolks and sugar until well combined, then add the cornstarch.
  • Pour the warm mango mixture onto the eggs, whisking vigorously, so that they don’t scramble. Pour everything back into the saucepan and bring to a slow boil, while continuing whisking, to avoid lumps. Cook for a couple of minutes. Remove from the heat, add the butter, salt, then the rum. Whisk until well combined. Place in a medium bowl, cover with plastic wrap at contact and refrigerate.
  • For the salted caramel sauce
  • In a small microwave safe bowl, warm up the heavy cream. Place the sugar in a saucepan, and heat over medium heat. Slowly melt the sugar until it reaches a dark amber color. 
  • Remove the pan from the stove and slowly pour in the cream while whisking it slowly. Be careful because it will splatter. If the caramel seizes up on you – because the cream is too cold of you poured it too quickly – just return the mixture to a low heat and cook it until the sugar crystals are fully dissolved.
  • Add butter and salt. Whisk the mixture until the butter is fully melted. Transfer the the sauce into a bowl and cool completely.
  • For the caramel Swiss meringue buttercream
  • Place the egg whites, sugar, and salt in the bowl of a stand mixer and whisk until well combined. 
  • Set the bowl over a pan of simmering water (the base of the bowl should not touch the water) and whisk constantly until the mixture reaches the temperature of 150 degrees Fahrenheit on a sugar thermometer. 
  • Remove the bowl from the pan and put it in place on the mixer fitted with the whisk attachment. Whisk on high speed to make a thick white meringue. Keep whisking until the meringue has cooled to room temperature, then start adding the butter by the tablespoon, until it’s all incorporated and the buttercream is smooth and silky.
  • Add the caramel sauce in three batches, and keep whisking until light and fluffy. Set aside.
  • For the coffee walnut cupcakes
  • Preheat the oven to 350 degrees Fahrenheit. Line two muffin pans with baking cups – you should have 18 to 24 cupcakes. Set aside
  • Put the walnut pieces and the sugar in a food processor or a coffee grinder, and grind to a fine powder. In a bowl of a stand mixer with a paddle attachment mix the walnut mixture, the butter, flour, baking powder, baking soda, salt, and eggs, until you obtain a smooth batter.
  • In a small bowl, combine the buttermilk, espresso powder, vanilla, and glycerin. Add to the flor mixture and beat until well combined and smooth, scraping down the sides when necessary.
  • Drop dollops of the batter in the baking cups, filling them 3/4 of the way. Bake in the oven for 20 to 25 minutes, until they spring back when touched. Coll on a cooling rack for 10 minutes, then remove from the pan to cool completely.
  • To assemble
  • With a cupcake coring tool, or with a knife, make a whole in the center of the cupcakes, making sure to leave at least 1/4 inch of cake at the bottom. Mix the mango curd until smooth, and drop in the center of the cupcakes. ,Close the hole with the top of the cake you removed early.
  • Place the caramel Swiss buttercream in a piping bag with a star tip. Decorate the cupcake, and drizzle with leftover caramel sauce, if you’d like.

Follow for more gluten-free recipes and weekly updates!

Tag @Simona.glutenfree on Instagram and hashtag it

Like this recipe?

Follow us @simonaglutenfree on Pinterest

Did you make this recipe?

Follow us on Facebook

Leave a Reply