Lavinia Fontana, 16th century Italy
From One Year One Painting a Day.
One wonders how long she had to stand for this portrait. The boy apparently wouldn't stay put for long, because his face is rather more sketched. I also find it interesting that 16th century hands are always delicate and arching, regardless of body structure. The wiki entry linked above has a slimmer portrait from Bianca's youth, which offers an interesting contrast.