The beef is the lean part of the plate. Long Chau lists lean beef at 147 calories per 100g and fattier cuts at 239 to 306, and a bo ne portion is 80 to 100g of thin sliced round or flank, about 170 once marinated in oil and oyster sauce. What takes the plate to 680 is everything around it: a fried egg at 100, 15g of pate at 50, one xiu mai at 70, and a knob of butter plus oil on the iron plate at 90. That is 310 of extras before the bread.
The banh mi is the other 190, and a lot of quan put two on the table. Dip both into the egg yolk and pate and you are at 870 for breakfast. Bo ne dac biet adds a sausage and a second egg, another 200. Long Chau's warning that a full plate with sausage, egg, pate, bread and potatoes gets close to 1,000 calories is about right for the big 65,000 dong versions.
It is a good protein breakfast if you strip it back, 38g on the standard plate. Bo ne with just beef, one egg and one bread is about 480 and keeps you full until lunch, which is the opposite of a 360 calorie banh bao. The cast iron plate is the thing to watch: whatever butter is left on it at the end got absorbed by the bread you wiped it with, and 10g of butter is 75 calories.