Preheat oven to 325 degrees. Place butter on a 15 1/2 x 10 1/2-inch jellyroll pan; place in oven to melt butter, about 7 minutes. Meanwhile, beat egg whites with salt until frothy; gradually add sugar, beating to stiff peaks.
Gently fold in almonds and cinnamon. Pour almond mixture onto jellyroll pan; toss with butter. Bake about 40 minutes, tossing every 10 minutes, until almonds are crisp. Serve warm or at room temperature. Store cooled in air-tight containers up to 2 weeks.
Preparation time: 10 minutes Cooking time: about 50 minutes