Bring a pot of water up to a boil and salt generously. Trim asparagus and add to water. Blanch, uncovered, until tender (check by tasting – time will vary depending on thickness of asparagus).
Once tender drain and shock in a bowl with ice and water to halt cooking. Strain and chill until ready to serve.
For hollandaise, stir rhubarb, sugar and tarragon sprigs in a pot over medium heat. Simmer until rhubarb is just tender, about 10 minutes. Remove tarragon and keep warm (but not hot).
To assemble Hollandaise, whisk egg yolks and lemon juice over a pot of gently simmering water until they hold a ribbon when the whisk is lifted. Whisk in rhubarb mixture to warm.
Remove bowl from heat and gradually whisk in melted butter (try to avoid adding white solids that have settled to the bottom of the butter).
Season to taste and keep warm (hollandaise should be prepared as close to serving as possible)
To heat asparagus, simply warm in a sauté pan over medium-low heat with butter and season lightly. Place warm asparagus on a platter and spoon hollandaise over. Garnish with chives and serve immediately.