Line an 8x8 or 9x9 inch pan with parchment paper. Set aside.
In a large pot, melt the butter over medium heat. It will start to crack and sizzle - let it do this while stirring occasionally.
After a few minutes or so, the butter cracking and sizzling will subside and it will foam up in the pan. Once you see the foam, add the milk powder and whisk vigorously to combine.
Every few seconds or so, swirl the pan around until you can see that the butter is golden brown. You should also be able to see some of the brown bits swirling around in the butter.
Immediately turn off the heat and add the marshmallows. This will prevent the butter from browning any further. Stir to coat the marshmallows completely in the butter until they begin to soften, about one minute.
Turn the heat back on low, add the salt and vanilla and stir. Continue to mix until the marshmallows are almost smooth. You want the marshmallows to melt evenly and gently so they are soft all the way through without boiling. If the mixture reaches a boil, the sugars can crystallize forming a harder Rice Krispie Treat.
Once completely melted, add the cereal and chopped Oreos and use a rubber spatula to fold everything together until the cereal and Oreos are coated. Remove from the heat.
Pour the mixture into the baking pan, gently packing the mixture into an even layer. You don’t want to pack too much, otherwise you could turn a delicate and fluffy treat into a packed and hard one.
Top with more crushed Oreos. Let cool and set for one hour at room temperature.
Once set, slice the treats into 9 large pieces or 16 smaller pieces. Store in an airtight container at room temperature.