Pulse the freeze-dried pineapple chunks in a food processor and pulse several times, or until it becomes a fine powder. Measure out 1 Tablespoon of this powder.
Place 1 cup American Buttercream in a medium mixing bowl. Add the 1 Tablespoon freeze-dried pineapple powder, pineapple juice, and the Junket Ice Cream Mixture. Mix well. If buttercream is really stiff, add 2 teaspoons heavy whipping cream, 1 teaspoon at a time.
Place into piping bag. Pipe a ring onto macaron shell, and place a matching-sized shell on top, pressing down slightly to adhere it well, but not so hard that the filling oozes out the side.
Store in refrigerator to mature for 12-24 hours before serving. After the maturing process, you can store in the freezer for up to a month.