Hi Katie,
I do not recommend doubling any recipe or changing the quantity of ingredients. Baking is a science, and you’ll get completely different results. To double this recipe, use 2 egg yolks. I have a whole section on my site for what to do with leftover egg whites: https://www.dessertfortwo.com/category/egg-white-only/
You should try anyway, since it’s just a small batch. Practice makes perfect :)
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