Once the eggs and vanilla are fully mixed in, add in the flour, baking soda, salt and cinnamon. Mix in until it just comes together. Be careful not to overmix the dough, because it would make the cookie tough.
I have a small ice cream scoop that I use, to scoop out the dough, so that the cookies end up being roughly the same size. You can easy use a spoon to dole them out, its really whatever works easier for you.
And after they bake (for 10-12 minutes), they are going to be a pale, light brown. If you use a dark brown sugar, they will be a more golden brown, but I used light brown sugar, so these are a pale golden brown.
Let them sit on the baking sheet after they come out of the oven for a couple of minutes, then move them to a cooling rack to cool fully before getting to the ice cream sandwich part! You can certainly stop here, and just have some amazing, tender cookies if you'd like, but I do like to take them that one step further. Now, that being said, these make about 4 dozen cookies, so unless you want to make a ton of ice cream sandwiches, you'll have a lot of cookies leftover!
Once they have cooled completely, take out a square of plastic wrap, about 8"x8", and find two cookies that are roughly the same size.
The easiest way to get a perfect sized slab of ice cream onto a cookie, is to just cut into the ice cream carton directly, and place it on the cookies. Once you cut through the carton, gently press the ice cream through the ring of the cut carton, and it falls out onto the waiting cookie.