Line an 8×8-inch or 9×9-inch baking pan with aluminum foil and spray with cooking spray; set aside. Note – I made the fudge in an 8×8-inch pan and it’s very thick/tall. For fudge that’s not as thick, use a 9×9-inch pan which is what I’ll do next time.
To the canister of a food processor fitted with the S-blade, add the Oreos and mix on high speed until you have fine cookie crumbs.
Add the butter and mix on high speed until combined.
Turn crumbs out into prepared pan and hard-pack them with a spatula to form and even crust layer; set aside. Optionally, bake in a 350F oven for 10 minutes to help crust set better and not be as crumbly as the no-bake method.
To a large, saucepan add the white chocolate chips, sweetened condensed milk, butter, and cook and stir over medium heat until the white chocolate chips are melted and the mixture is smooth; stir nearly constantly and be patient because white chocolate chips can be resistant to melting.
Add the pudding mix and stir until combined.
Turn the heat to low, add the marshmallow creme, and stir continuously to combine, about 1 minute (your shoulder will be burning because mixture is very thick). Remove from the heat and immediately pour the mixture over the prepared crust.
Top with sprinkles and place pan in the fridge to set up, at least 2 hours or until set and firm. Fudge needs to be refrigerated and will keep airtight in the fridge for up to 1 week or in the freezer for up to 2 months.