By substituting Frangelico for vanilla extract, the hazelnut flavor is not too overpowering, but it makes it taste like the richest chocolate you’ve ever had.
Preheat the oven to 225°
Meanwhile, fill medium saucepan one quarter full with water. Set the saucepan over medium heat, and bring water to a simmer. Combine egg whites, sugar, and cream of tartar in the heatproof bowl of electric mixer, and place over saucepan. Whisk constantly until sugar is dissolved and whites are warm to the touch, 3 to 3 1/2 minutes. Test by rubbing between your fingers.
Transfer bowl to electric mixer fitted with the whisk attachment, and whip, starting on low speed, gradually increasing to high until stiff, glossy peaks form, about 10 minutes. Add Frangelico, and mix until combined. Gently fold in the cocoa powder.
Using a small spoon, portion the mixture onto baking sheets lined with parchment paper. Bake until the cookies life off of the parchment easily, about 2-3 hours. Yes, that’s a really long time, so please don’t do this on a hot day, okay?