Push blender to bottom of cup, and blend WITHOUT LIFTING until garlic, salt, and lemmon juice start to form a white emulsion.
After emulsion has formed, start lifting blender a bit to blend in some oil, a little at a time.
Continue to lift, stir, and blend until all oil has been whipped into the emulsion and it thickens.
I was having the blender cavitate (get air in the blender area) when emulsion thickened, and it
became hard to blend farther.
When thickened in this manner, Toum is ready.