Drain and rinse beans. Bring to a boil in a medium saucepan of water; boil, uncovered, about 15 minutes or until very tender. Drain.
Meanwhile, combine oils, rosemary and garlic in small saucepan. Heat over low heat until garlic just begins to turn golden, about 3 minutes. Remove from heat; stand 10 minutes to allow flavours to infuse into oil. Discard rosemary; remove garlic; reserve if desired.
Place beans in a blender. Squeeze garlic from skins and add to beans if desired. Pulse beans (and garlic if using) with half of the oil until starting to blend easily. Add remaining oil in a steady stream until all incorporated and mixture is very smooth.
Add lemon juice and salt to taste. If bean puree is too thick; add a little water to thin to desired consistency.