Hi Deborah, this isn't something we've tried, but we think adding 3/4 of a cup of rum or Kahlúa might be a bit much, so we would suggest adding up to half a cup of either rum or Kahlúa and making up the difference with water. And since rum and Kahlua aren't particularly acidic ingredients, you'll probably also want to add 1 1/2 teaspoons of vinegar to this version of the recipe. If you use a dark liqueur, keep in mind that the cake may be slightly beige or grey in color. 

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