Place a heavy-bottomed pot on the stove over low heat. Inside the pot, put the butter to melt.

When the butter is melted, add half of the marshmallows and the vanilla essence. Stir occasionally.

Cook the marshmallows on low heat for about five minutes.

Cotinue cooking until all the marshmallows have melted and the marshmallow and butter mixture is smooth.

Then add three cups of the puffed rice, the chopped oreo cookies, the chocolate chips, and the rest of the marshmallows. Stir for a couple of minutes with a spoon until all the ingredients are combined.

Lightly grease a square or rectangular non-stick pan, preferably silicone. We use a 25 cm square mold. Pour the mixture on top of the mold. Spread it out with a spatula. Then, add the remaining cup of puffed rice on top, distribute well. Compact the mixture, pressing it down, you can use your hands, or a potato masher.

Take the mold to the refrigerator for at least an hour. After the mixture has hardened, remove it from the mold, and cut it into regular pieces with a bread knife.

Note: When the krispie treat mixture is still hot it is sticky, and a bit difficult to handle. One trick I usually use when making krispies treats is to reserve a cup of puffed rice for when I put the mixture in the mold. I sprinkle all the puffed rice on top, and compact the mixture with a kitchen spatula. This helps the mixture not stick from the spatula.