No Bake Cookies (impossible!)

This is my Mom's recipe and I've now been put in my place twice by it.

Mom's Famous No Bake Cookies

Melt 1/2 cup Butter in pan -- low heat
Add in 1/2 cup Milk or Half and Half -- more fat = more taste
Add in 2 cups Sugar
Add in 1/3 cup powdered baking Cocoa
Add dash salt Salt
Stir until it all melts together (medium heat then warmer to get to right temp)and reaches 200 degrees
Add 1 & 1/2 handfuls mini-marshmallows
Stir until slightly melted, remove from heat
Add 1/2 cup Peanut Butter -- stirring
Add 1 tsp Vanilla -- stirring
Add 2 cups Oats -- stirring
Keep Stirring
Could add other things (cranberries, other fruits, nuts, etc)
Spoon onto waxed paper immediately

My Place: NOT IN THE KITCHEN!

This recipe doesn't seem too bad, and I usually can follow directions, but I've been foiled twice now. First time I used quadruple the amount of milk, causing everything to be off -- that turned into a chocolaty soupy mess. Note to self -- adding quadruple extra oats to make up for quadruple extra milk does not work. The second time I thought everything was going good. It all boiled, I had the right amounts ... but now the darn things won't harden. They are stuck in a limbo-like state between a cookie and yogurt. This is not a place you want your cookie to be. I think next time I need more heat ... until then, I bow to the "no bake cookie" cooking prowess of Mom.

...

An Update -- 3rd time was the charm. I can rock this recipe now.