I have continued my pipeable marshmallow experiments and want to report what was successful. The recipe below is based on the RecipeGullet one for strawberry marshmallows, with adaptations for piping. I have converted the measurements to grams.
Notes: The tricky part of the process is getting the marshmallow to a low enough temperature that it will not melt the chocolate shells but not so low that it starts to set. In practice I found that if you keep piping, that window is wider than it might seem. I suspect the heat of one's hands on the piping bag helps, and one could always give a little boost with a heat gun. A larger amount of marshmallow might present problems; therefore the amounts are half of the RecipeGullet ones. I think the reason my earlier attempts failed is taking the syrup to a higher temperature; with the 235F/113C specified here, the mixture is easily pipeable and does not leave a trail of marshmallow over the top of the mold. It is worth mentioning that the marshmallow loses its pink color as it is beaten.
PIPEABLE STRAWBERRY MARSHMALLOW
Mix 14g (2 envelopes) unflavored gelatin with 120g strawberry purée (strained to remove any pulpy parts) and (if desired) 1/8 tsp. orange flower water and (if desired) 1 tsp. strawberry compound in a small bowl and place over hot water. Make sure all the gelatin is dissolved.
Meanwhile put 300g sugar, 185g glucose, and 100g water in a heavy pot. [Edited 4/20/2018: From a suggestion made by Pastrypastmidnight, I now substitute 100g of strawberry purée for the water--a change that substantially enhances the fruit flavor.] Over low to medium heat stir until the sugar is dissolved, washing down any crystals on the side of the pot. Let the sugar mixture boil until it reaches 235F/113C, then remove from the heat and allow to cool until the temperature is 212F/100C. During this time be sure to keep the gelatin mixture warm.
Transfer the gelatin mixture to the large bowl of a mixer with a whisk attachment, turn on the mixer, then slowly pour the syrup down the side of the bowl. Gradually increase the mixer speed to high. When the marshmallow is very thick, start testing its temperature. For piping into molds, it should fall to around 92F/33C (this assumes further cooling as it is transferred to a piping bag). Beat the mixture at slow speed while waiting for it to cool. [Edited 5/29/2020: I now fill a large plastic bag with ice cubes and hold it against the side of the mixing bowl; it lowers the marshmallow to a pipeable temperature quickly. I have also discovered that waiting to add flavoring (vanilla, purée, etc.) until the end of the beating thins out the marshmallow enough that it pipes easily and even self-levels in the cavities. After a day of standing, it had formed a skin on top that made piping an additional layer easy. When I measured its water activity level, it was 0.78, higher than when adding flavoring earlier but still acceptable for most people.]
With an oiled spatula transfer the marshmallow to a piping bag and pipe into molds. The piping should be done as quickly as possible (at 86F/30C the gelatin begins to set). Allow the marshmallow to set at least 12 hours before adding a second layer or closing the mold.
Approximately 90-100 cavities (15g size) can be fully filled with this recipe.
