Potter wasp nursery chamber, but what kind?

Observation - Potter wasp nursery chamber, but what kind? - Global. Description: A friend in France found this on the south side of his house, about a metre and a half up from ground level. Seems to be made of fine sand and silt. He saw a smallish wasp fly up to, and stick its head up to the opening. The wasp was maybe 3/4 inch long,

A friend in France found this on the south side of his house, about a metre and a half up from ground level. Seems to be made of fine sand and silt. He saw a "smallish wasp fly up to, and stick its head up to the opening. The wasp was maybe 3/4 inch long, small, but much too big to get even its head into the opening. I presume the hut to be a nursery."