Scaling Up the Recipe for 8-inch Tins

• This recipe is sufficient for 3 sponge cakes baked in 6-inch tins. Do not try stretching the recipe to fill 8-inch tins - the layers will be too thin
• Ideally, scaling up to a 5 egg recipe is required for 3 layers of 8-inch cakes. However, that gives some fiddly measurements, so I suggest simply doubling the recipe, filling your cake tins ⅔ full then using any surplus cake batter to make a few cupcakes
• As for the buttercream, you will not need to double this. Instead, go for 9 egg whites/ 600g sugar / 675g butter

Baking Tips

• Please use digital scales for this recipe as they are so much more accurate than the cup system. Cups are notoriously inaccurate because they can vary in size and one person's method of filling a cup can be quite different to another person's
• Regardless of whether your tins claim to be non-stick always grease them and use a circle of baking parchment to line the bases. These 2 steps help ensure the cakes never get stuck in the pan
• Preheat the oven and prepare the baking tins before baking commences so that the cake layers can go into the oven as soon as the batter is mixed and the raising agent (baking powder) is activated. You'll get the best rise this way
• Let the cakes rest in their baking tins for 2 minutes once they are taken out of the oven. They will shrink slightly, pulling away from the edge of the tin. This helps get them out of the tins more easily
• Don't under-estimate the time it takes to make the buttercream - allow at least 45 minutes and up to 1 hour (but it's ok, the stand mixer does the hard work)
• I do not recommend making this buttercream by hand -  you'd be beating for hours
• On this note, I once made SMB using a handheld whisk, but that took 45 minutes of standing around holding the beater, so again, I'd really only recommend using a stand mixer for this buttercream. If you do not have one, simply make the cake and use an alternative buttercream as suggested in the tips section in the post above
• Depending on the brand of coffee used, the coffee Swiss meringue buttercream may discolour if stored at room temperature, although it's still safe to eat and the flavour remains unaffected
• There is a risk that the buttercream will darken and/ or discolour if left at room temperature. Either frost your cake just 2-3 hours prior to serving or store in the fridge and bring it back to room temperature before serving. Alternatively, use a different frosting completely (see my suggestions in my blog post)

Troubleshooting

• If you've been beating the meringue for a long time and it refuses to reach the stiff peak stage the most likely reason is that a spot of egg yolk accidentally made its way into the bowl. Even the smallest amount will prevent the whites from whipping up and sadly, there is no way to rectify this issue other than starting again
• Likewise, any grease in the bowl will have the same effect. For this reason, ensure your bowl and beaters are perfectly clean before starting
• If your buttercream mixture appears thin and runny after adding the butter, this is because either the butter or the meringue was too warm when the butter was added. But the fix is easy - place the mixing bowl in the refrigerator (covered) for 20 minutes to cool down, then continue to beat until thickened. If it's still too thin, return to the fridge for another 20 minutes and try again.