Preheat the oven to 225ºF and line a large baking sheet with parchment paper.

In a medium bowl, whisk together the egg whites, maple syrup, vanilla extract, and cream of tartar.

Transfer the mixture into a double boiler and continue to mix until the temperature reaches 140ºF. This should take about 5 minutes.

Remove the pan from the heat and use an electric mixer to beat the mixture into stiff peaks, about 6 minutes. The ideal mixture should have a glossy marshmallow texture.

Spoon mounds of meringue onto the prepared baking sheet. Make sure to space about 2 inches apart.

Sprinkle the cookies with hazelnuts on top and bake for 1 hour and 30 minutes.