Add the butter in a large pot, and melt over medium heat. When melted, reduce the heat to low and whisk in marshmallows. Once the mixture has completely melted, stir in salt and puffed rice cereal.

Line a 9 x 13 inch pan with parchment paper. Press the puffed rice mixture into the pan and let set for 30 minutes.

Meanwhile, make cookie dough by creaming softened butter with sugars in a medium bowl with an electric mixer or in the bowl of a stand mixer fitted with the paddle attachment. Once pale and fluffy, add milk, vanilla, salt, and flour. Mix until dough forms. Fold in mini chocolate chips.

Spread cookie dough over set puffed rice mixture. Refrigerate 30 minutes, or until cookie dough sets.

Slice into squares.

Melt the white chocolate and dark chocolate in the microwave or over a double boiler. Dip rice krispie treats into melted chocolates and decorate with sprinkles. Refrigerate until chocolate hardens.

To make mummies: Dip rice krispie treats into the melted white chocolate, making sure to coat all sides. Place on a parchment lined baking sheet. Place treats in refrigerator for 5 minutes for chocolate to set. Fill a small zip top bag with remaining melted chocolate. Snip a tiny bit off one of the bottom corners. Drizzle chocolate over treats in a zig-zag patten to create "mummy" look. Add 2 mini chocolate chips for eyes and return to refrigerator for another 5 minutes. Serve, or store in an air tight container for up to 1 week.