À la boulangère is a French cooking term that means literally “in the manner of the baker’s wife.”
It is usually something baked, as the phrase “baker’s wife” would imply access to and use of an oven (and remember, such access was until relatively recent in history not very common.)
You can expect a garnish of potatoes and onions that would have been cooked alongside the meat, which is usually lamb, mutton or poultry. There would be no sauce other than the juices from the meat.