Line a 9×13-inch (23×33 cm) baking dish with parchment paper, leaving an overhang on two sides for easy removal, or lightly grease the dish with butter. Set aside.
In a large pot or Dutch oven set over medium-low heat, melt the butter completely. Once melted, add the dry sugar cookie mix and fine sea salt and stir until smooth and fully incorporated, with no visible lumps.
½ cup (113 g) unsalted butter, ⅓ cup (55 g) dry sugar cookie mix, ½ tsp (3 g) fine sea salt
Add 9 cups (510 g) of the mini marshmallows and cook, stirring constantly, until the marshmallows are fully melted and the mixture is smooth. Keep the heat low and stir continuously to prevent scorching or caramelization.
10 cups (569 g) mini marshmallows
Remove the pot from the heat and immediately stir in the vanilla extract and almond extract until evenly combined.
1 tsp (5 ml) vanilla extract, ½ tsp (2.5 ml) almond extract
Add the Rice Krispie cereal along with the remaining 1 cup (57 g) of mini marshmallows. Stir gently but thoroughly until the cereal is evenly coated and the reserved marshmallows are distributed throughout.
8 cups (234 g) Rice Krispie cereal
Transfer the mixture to the prepared baking dish. Using a piece of parchment paper or lightly buttered hands, gently press the mixture into an even layer. Do not compact it tightly, as this will result in dense treats.
While still warm, sprinkle the top evenly with holiday sprinkles and gently press them in so they adhere.
holiday red and green nonpareils
Allow the treats to cool and set at room temperature for at least 1 hour. Once fully set, lift from the pan using the parchment overhang and cut into squares using a sharp knife or bench scraper. Lightly grease the blade, or warm and dry it between cuts, to achieve clean edges.