The first step is to melt the marshmallow fluff and butter. You can do this on the stove, but the microwave is much faster and easier. Put them in a glass bowl for a minute or so.
Take the bowl out of the microwave (carefully – it's hot) and stir it up. If your marshmallow fluff looks fluffy, like this does, it needs to go back into the microwave for another minute.
Remove the bowl and stir again. If it is sufficiently melted, the goo will be a liquid. Make sure the butter is incorporated with the marshmallow liquid.
Pour the marshmallow liquid into the Rice Krispies and mix them until it's completely distributed through the cereal.
At this point, I thought we could form the sticky Rice Krispies into nest shapes, set them on foil to dry, and be done. I grabbed a handful of the mixture, and I squeezed it.
And then I opened my hand, expecting to find a nest. I was wrong. Instead, the sticky Krispies stuck to my fingers and spread out again. Grace and I looked at each other. We knew it was possible to make nests, but we had no idea how to actually make them. I suggested that we let the mixture sit a while (hoping it would get stickier), but Grace didn't want to wait.
I decided that a muffin pan would give us the right shape, but I was worried about the sticky nests getting stuck in the wells of the pan. We had used up all the butter in the house in step one, so I couldn't grease the wells. We had paper cupcake liners, but I thought they would stick to the nests. I decided on foil. I cut the foil into rectangles, and Grace pressed the rectangles into the wells of the muffin pan.
Together, we spooned the sticky mixture into the wells and left them to firm up a bit.
Then! We discovered our fancy muffin cups. I wish we'd thought of these to begin with. They were really pretty with the nests in them.
Grace did the rest all by herself, while I was working. After the krispies had dried and were no longer sticky, she pressed a little well into the center of each nest. She dropped a couple of jelly beans into each one.