Over medium heat melt the butter in the small saucepan.
Stir the butter occasionally. After the butter has melted it will start to get foamy, this is normal. You can even hear some crackly noises that butter makes.
Butter will change color to darker orange. You will see littel brown bits to form at the bottom of the pan.
Let the butter continue to brown for a few minutes.
Remove butter from the heat and transfer into bowl. Allow to cool and place in the fridge until soft.
In the bowl of stand mixer beat the butter until it is soft and creamy.
Add sifted powdered sugar and beat again untill fully combined.
If the buttercream is too thick add heavy cream or milk, 1 tablespoon at a time untill it reaches the desired consistency.
Transfer the brown butter buttercream to a pipping bag with pipping tip.
Pipe buttercream on flat side of macaron shell and sandwich with another macaron shell on top.