Lightly coat a large nonreactive bowl with nonstick spray. Add popcorn and almonds and toss 'em around to mix and combine.

Combine sugar, butter, and ¼ cup water in a medium saucepan. Bring it to a boil, and dissolve the sugar by stirring. Once the sugar has dissolved and the mixture is clear, cook until mixture begins to caramelize in spots (no stirring this time!), about 3 minutes. Continue to cook, stirring occasionally with a heatproof spatula to ensure even caramelization, until caramel turns a light amber, about 4 minutes.

Using a heatproof spatula, stir in marshmallows, rosemary, salt, and cayenne (if you're using it). Cook while occasionally stirring until the caramel is smooth, about a minute.

Take the pan off the heat and stir in baking soda (expect some bubbles from the mixture). Immediately pour over the popcorn mixture from step one and toss with 2 heatproof spatulas (the caramel's gonna get really sticky and stringy). Spray your hands with nonstick spray and form popcorn mixture into 2" balls (you should end up with about 14 balls). Transfer to a rimmed baking sheet and let sit at least 30 minutes before serving.