Preheat the oven to 275°F.
Beat the egg whites until they become foamy.
Gradually add the sugar while continuing to beat on high speed until the mixture thickens and turns glossy, about 2-3 minutes.
The mixture will not form stiff peaks but will become thicker.
Add in the vanilla and cinnamon, beating until fully incorporated.
Gently fold in the mixed nuts.
Place 1/2 cup of butter on each baking sheet (use a sheet with sides, such as a jelly roll pan or baking stone) and place them in the oven until the butter melts.
Once melted, remove the baking sheets and spread the coated nuts in a single layer, dividing them evenly between the two sheets.
Bake for 20 minutes, then stir.
Continue baking for another 15 minutes, stir again, and repeat this process until the meringue on the nuts turns golden brown and the butter is fully absorbed, which should take about another 30 minutes.