This demonstrates my memorization exercise, where I used an image from plate I-3 from the Charles Bargue plates.
The profile is of the great Italian poet Dante Alighieri. Notice the vertical plumb line and the points where the profile outline touches the plumb line. You can see me building up the drawing here, going from touch point to touch point. Memorizing the single-line segments independently is easier.
Practice the eyes separately—see lower part of the image.
And then I can put the whole thing together.
In the end, it is satisfying for me to be able to draw the entire profile from memory, seemingly from imagination.
You can also draw along with this YouTube Video: