Spray an 8×8-inch baking dish with nonstick cooking spray. Set aside.

In a large pot over medium heat, melt the butter. Add sweetened condensed milk and molasses, stirring well to combine. Bring the mixture to a gentle simmer, stirring constantly to prevent scorching.

Add marshmallows, stirring frequently until fully melted and smooth.

Remove the pot from heat and immediately stir in cinnamon, ginger, cloves, nutmeg, and kosher salt. Mix until the spices are fully incorporated.

Fold in the crispy rice cereal using a rubber spatula sprayed with nonstick spray. Stir until the cereal is evenly coated with the spiced marshmallow mixture.

Transfer the mixture into the prepared baking dish and press it into an even layer using the spatula (or your hands lightly greased or sprayed with nonstick spray).

Let the bars cool completely at room temperature before cutting into squares and serving.