This recipe is what I learned from TV a year ago. The original broth is 3 can of chicken and 1 can of beef. I cut the size for two person instead of four. (I will skip the beef broth if I don't have at hand.)
Easy onion soup
1) chop two medium size onion bulb into 1cm x 1cm cube
2) add two teaspoonful of butter into pan
3) cook onion to light brown on medium fire
4) add 1 can chicken broth and ¼ beef broth
5) cook to boil for 10 minutes
6) add seasonings (if necessary)
7) pour content into soap cups and add a load of bread
8) add mozzarella cheese slice on top
9) bake top to light brown at 300 deg F