Melt the butter in a Dutch oven or large stockpot over medium-high heat. Add the bacon and cook, stirring occasionally, until starting to brown, about 3 – 4 minutes. Add the garlic and sage, lower the heat to medium-low and continue to cook, stirring frequently, for an additional 1 – 2 minutes or until fragrant. Add the artichokes and sauté for 5 minutes, stirring well to combine all of the ingredients. Add the chicken stock to the pot and top up with enough water to completely submerge the artichokes. Bring to a boil and reduce to a simmer over low heat. Simmer, partially covered, until the artichokes are tender when pierced with a knife, about 20 minutes. Remove from the heat.
Working in batches in a standing blender, blend the soup until smooth. Return the soup to the pot and rewarm. Ladle into bowls and top with some crumbled blue cheese and freshly ground pepper, if desired. Serve warm.
Jerusalem artichokes have no relation to Jerusalem or to artichokes. How they got this name is a mystery. They are also known as sunchokes, sunroots and here in France they are called topinambour. They are related to the sunflower species and are usually cooked in ways similar to potatoes.