To fix a broken hollandaise, place 2 T cold water into a small bowl or shot glass. Add a little bit of the broken hollandaise to the cold water and mix well. Pour just a bit of the mixture into your pan of broken hollandaise starting at one edge of the pan. Stir vigorously with a small whisk until it reincorporates the broken hollandaise. Increase the size of your stirring just a bit to bring in a little more broken sauce. Once that part is incorporated, bring in more sauce. Continue until all of the sauce has come back together. It should hold together although sometimes it will separate again but it usually holds together long enough to serve. Don’t add too much of the water mixture in, you only need a little bit.