- In a bowl, combine the gelatin and water and let soften. Set aside.
- Butter a 23×33-cm (9×13-in) glass pan and dust the bottom and sides with 15 ml (1 tablespoon) cornstarch.
- In a heavy-bottomed saucepan, combine the maple syrup and cream of tartar and bring to a boil without stirring until a candy thermometer registers 120°C (250°F). Put a wooden spoon in the saucepan to prevent the mixture from bubbling up and overflowing.
- Stir the hot maple syrup into the gelatin. Add the salt and vanilla.
- Beat with an electric mixer until the mixture thickens, turns white and falls in ribbons (when you lift the whisk, the mixture stretches and falls gently back into the bowl like a ribbon).
- Pour into the prepared plan, level with a buttered spatula and let cool 3 hours at room temperature.
- Unmould onto a surface dusted with the remaining cornstarch, cut into cubes or cut shapes with cookie cutters.
- Maple marshmallows will keep for several days in an airtight container between sheets of parchment paper.
Maple Marshmallows will kept for several days in an airtight container, between sheets of parchement paper.