Can I halve the Amish Friendship Bread recipe?
Okay, I usually don't answer my own questions but by the time I got done writing up my question the answer came to me: 


On day 1 take your one portion of starter and divide it in half. The other half can either be shared with a friend or thrown away. (I promise I won't tell!)
On day 5, instead of adding 1 cup of milk/flour/sugar just add 1/2 a cup of each.
On day 10, instead of adding 1 cup of milk/flour/sugar just add 1/2 a cup of each.
Don't forget to mush/mix the bag each day.


Now on day 10 you'll have two regular sized portions of starter. You could use it to make two loaves of bread. Or you could use one portion to make one loaf, take the other portion and start again with step 1 above.