Spray a 9-inch by 13-inch cake pan with Pam (or line it with heavy-duty foil and then spray it) and set it aside to wait for its yummy contents.
Melt the butter in a small microwave-safe bowl on HIGH for 50 seconds.
If you bought chocolate wafers, break them down into crumbs with your food processor or put them in a large, sealable plastic bag and crush them with a rolling pin. Measure out the chocolate wafer crumbs (or the Oreo cookie crumbs) and add them to the bowl with the melted butter.
Stir the cookie crumbs and the butter until everything is moistened. (The resulting mixture will resemble wet, dark sand.)
Spread the butter and cookie crumb mixture in the bottom of your cake pan and spread it out as evenly as you can.
Pat it smooth with the palms of your impeccably clean hands or with the blade of a metal spatula.
Sprinkle on the semi-sweet chocolate chips. Try to distribute them as evenly as possible.
Arrange the miniature marshmallows on top of the chips as evenly as you can.
Open the can of sweetened condensed milk and pour it over the top of the marshmallows as evenly as you can.
Sprinkle the white chocolate chips on top, trying for an even distribution.
Your goal is to get something of every ingredient in each cookie bar when you cut them.
Measure out the Cocoa Puffs (or whatever chocolate cereal you used) and spread it out on top of the white chocolate chips. Again, try for an even distribution.
Sprinkle the milk chocolate chips over the chocolate cereal as evenly as you can.
Press everything in the pan down with the flat blade of a metal spatula or the bottom of a measuring cup. (If the cereal crunches a bit, that's okay.)
Bake the Chocolate Euphoria Cookie Bars at 350 degrees F. for 20 to 25 minutes.
Remove the cookie bars from the oven and cool them in the pan on a cold stovetop burner or on a wire rack.
When the Chocolate Euphoria Cookie Bars reach room temperature, cut them into brownie-sized pieces right in the pan. Don't take them out unless you're going to eat them immediately.
You can now refrigerate the cookie bars in their pan to set up firmly.
If you don't cut the bars before you put them in the refrigerator, you may have a problem. They're very firm when they're chilled.When you're ready to serve, use a metal spatula to remove the cookie bars from the pan. No one will be able to resist.