9 . Meanwhile , to prepare the cream cheese frosting , using the paddle attachment cream the butter , lemon zest , vanilla and salt for 2 minutes or until light and fluffy . With mixing speed on low gradually add the powdered sugar and lemon juice , beat until it forms a thick paste . Add the cream cheese and mix on the lowest speed possible for 1½ minutes , then STOP ! Place in refrigerator to chill for at least 15 minutes or until cupcakes have completely cooled . Allow to stand at room temperature for 5 minutes before placing in a bag to pipe on cupcakes .
10 . Using a large piping tip , pipe the frosting on top of the cooled cupcakes . Top with a slice of lemon and a sprig of mint , if desired .
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