According to the PHB, the Beast Master's companion acts on your initiative but can't attack, dash, disengage, dodge, or help unless you consume your action to command it to do so. That said, there is a clause stating:
Once you have the Extra Attack feature, you can make one weapon attack yourself when you command the beast to take the Attack action.
Does this clause circumvent the consuming of your action? Or is it trying to imply that once you have Extra Attack, you can use one attack to command your pet to attack, and the Extra Attack to attack yourself?
If the former, it would make the Beast Master Ranger feel much more balanced, since at 5th level you'll be able to attack twice and have your companion attack once. Without it, it seems almost worthless to go Beast Master, since your companion is always locked to 1/4 CR and having it attack would prevent you from doing anything that turn (whereas the other archetypes work to power you up, not down).
This seems like it would also bring the Ranger more in line with other classes (and the beast master more in line with other archetypes) without the need for a house rule like allowing the Beast Master to command their companion to attack as a bonus action.
Best Answer
You get one attack
You are not taking the Attack action so you don't get two attacks from Extra Attack (emphasis mine):
Instead, this feature gives you a separate benefit: "make one weapon attack" when you command your beast to Attack: