1.   At this point, reduce the speed to medium or low and add the room-temperature butter pieces, one at a time.

2.   Add the butter one piece at a time, blending again after each addition, to thicken the soup slightly.

3.   Add the chilled butter pieces, and pulse until the mixture resembles grated cheese.

4.   Add cubed butter and pulse mixture just until butter pieces are the size of lentils.

5.   Add half the butter pieces.

6.   Add the butter pieces.

7.   Add butter one piece at a time, whisking to emulsify the sauce.

8.   Add butter pieces and vanilla and process a few seconds, until mixture is crumbly and there are many pieces the size of large peas.

9.   Make sure butter is well incorporated and dough is stretchable without having visible butter pieces.

10.   Reduce heat to very low, and whisk in butter piece by piece.