To prepare hash: Mash potatoes until slightly chunky. In a large bowl, mix potatoes, carrots, beef, egg, sage and thyme until just combined. Season with salt and pepper to taste. Scoop 1/4 cup portions and form each into logs about I/2 thick.
In a medium sauté pan, melt 1 tablespoon butter and sauté spinach until wilted, about 3 minutes
Serve hash on a bed of sautéed spinach with poached egg on top and hollandaise sauce generously spooned over.