Finely chop shallots, chili, herbs, and tarragon. Then put them in the bowl with the butter. Squeeze the lemon. Add lemon juice and Dijon mustard to the bowl.
Knead and mix all the ingredients in the bowl with your fingers or a hand mixer.
Once the bearnaise butter is kneaded together, place it in the middle of a piece of parchment paper and roll it into a sausage or, as I've done, pipe it out onto the parchment paper. I think it looks more festive.
Put the bearnaise butter in the fridge. Let it cool for at least 20 minutes.