I don't make mine that way. I make on the stove with a wisk.
I think there is a recipe for a blender bearnaise sauce in one of the Barefoot Contessa cookbooks, if I'm not mistaken. I can't post a copyrighted recipe here but try a google search for that
I am a old retired Chef and have made Bernaise many ways and have found over the years that the whisk and bowl method is the best for consistincy
and taste.. But if you insist try this . in a medium stainless steel bowl over simmering water whip your egg yolks with a tsp of hot water and whip till you see threads in the yolk then switch to your imersion blender and very slowly add your butter (clarified ) and your tarragon vinegar reduction a little at a time check your seasoning and add the acid very carefully as it will break if to much to soon LOL Chef Dave