In brief
In King Arthur Baking's Italian Meringue Macarons, sugar syrup is prepared separately and streamed into whipping egg whites. The meringue then contributes to the almond shells.
Useful to know
In King Arthur Baking's Italian Meringue Macarons, sugar syrup is prepared separately and streamed into whipping egg whites. The meringue then contributes to the almond shells. [1]
This differs from adding all the sugar directly to egg whites. Follow the specific syrup and mixing instructions; the shared name macarons does not make methods interchangeable.
Sources
For further detail and to check the information: