How to make a supermassive black hole

Apparently, the recipe is:
Step 1 - Crash two galaxies together
Step 2 - Wait for the two smaller black holes at the center of these galaxies to merge together, during which time lots of gas falls into them.
Step 3 - Go to Step 1.

Figuring this out was not as simple as it looks. Go here,
here, and here, and here to learn more.