Why do my cookies fall flat and not cook on the bottom? I'm fairly new to baking, but I've been attempting to make cookies lately. They taste good, but come out looking like this:



The bottom looks like this:



They spread out a lot in the oven (they went in as balls ~1 inch diameter and came out as flat disks ~4 or more inches across) and don't really have a crust on the bottom. I used these ingredients:

1 stick butter
1/2 cup sugar
1/2 cup brown sugar
1 egg
1 tsp vanilla extract
1/2 cup pumpkin puree
1 1/2 cups flour
1 tsp baking soda
1/4 tsp salt
2 tsp pumpkin pie spice
~1/2 - 1 cup milk chocolate chips


To cream the butter with the white sugar I let it sit for about half an hour, cut it into small chunks, let it sit a little longer, and then alternated beating them with a fork and a hand mixer with beater attachments. I'm looking into getting a stand mixer. The dough for the pictured batch was chilled in the fridge overnight.

How can I keep them from spreading out so much and develop a crust on the bottom?

Edit: I baked them at 350F, fully preheated, for around 15 minutes on a bare cookie sheet. I peeked after about 8 minutes and then probably two more times after that before I took them out.
Welcome to Seasoned Advice first I will point you to an article in our blog Silpat, Parchment Paper or Plain Baking Sheet. @KatieK contrasts these cooking surfaces.Look at the instructions for time and temp. Are you thoroughly Preheating? You pictures indicate that you are using parchment, but you don't mention time/temp. 

My first inclination based on what I see is that you are baking them too long at too low a temp, and not fully preheating. If you raise the temp and shorten the time the cookie will not spread as far. With 'scoop' cookies you expect the dough to spread some, but you are getting too much spread. The higher temperature will cause the cookie to form a solid (ok, solidish, it should be soft but 'strong enough' to hold form) This will also give you better "bottoms" as they will bake faster as well. 

Another thing you might be doing is opening the oven door too often, this releases a lot more heat than you think, extending the correct baking time and slowing the process. I know it is sometimes hard to resist peeking, try to not open the door till you are at least 75% through the projected time.