Lightly butter a 9 × 13-inch baking dish or line it with parchment paper. Measure the cereal into a large bowl so it is ready to go once the marshmallow mixture is melted.
Melt the butter in a large saucepan over medium-low heat. Add the marshmallows and stir gently until they are almost completely melted. Reduce the heat to low and add the Michelle’s Mexican Mocha Mix, vanilla, and salt. Stir until the mixture is smooth and the mocha mix is evenly incorporated.
Remove the pan from the heat and immediately fold in the Rice Krispies cereal. Stir just until every piece is coated. If you're using mini chocolate chips, let the mixture cool for a minute or two before gently folding them in so they don't completely disappear into the marshmallow.
Transfer the mixture to the prepared pan. Using a buttered spatula or a piece of parchment paper, gently press it into an even layer. Don't pack it down too firmly—that's how innocent Rice Krispies treats become construction materials.
Let the treats cool for about 30–45 minutes before cutting them into squares. For a more finished Café-style version, drizzle the tops with melted chocolate and allow the chocolate to set before serving.
