How to prevent a cookie from becoming spongy like a cake?

They're definitely under cooked. The recipe calls for a 10 minute bake at 350 degrees -- that's seems short. You want to pull them when the edges are darker brown, which probably would have taken another 4-8 minutes.

It's hard to tell with the lighting of your photo, but I think your tops weren't browning fast enough either. Before I got a new oven, I'd have that same problem when I baked cookies. I fixed that by starting the cookies on a lower rack (one or two slots from the bottom) and moving them halfway through to a higher rack (one or two slots from the top).

Letting the cookies cool on the pan also helps set them hold together better.

EDIT: As for the texture -- you aren't going to get a crunchy cookie from this recipe. This recipe is for a slightly chewy cookie with crisp edges. If your cookie is still cakier than chewy, you may want to make sure you are measuring flour correctly.

Here are a few things that may really help:

Do not completely melt the butter. Allow it to just soften to the point where you can mash it with a fork.

Add butter to the mixer first. Let the mixer whip the butter til it gets slightly creamy then add other wet ingredients.

Add eggs 1 at a time.

For the eggs-the omega 3 eggs seem to be a bit fuller I dont know. And this could give the recipe more moisture and turn the cookies into a cake like texture. Try just regular eggs.

It's ok to use the whisk like attachment on the mixer when mixing the wet ingredients. Maybe switching to the cookie attachment or the dough hook once you start adding the dry ingredients to the mixture.

If you dont have the dough hook or cookie attachment. Just use a fork and start to fold the dry ingredients into the mixer and keep folding and lightly stirring with the fork.

Also check and make sure you are using all purpose flour for your cookie recipe. The tollhouse recipe calls out baking soda instead of baking powder. Also something to keep in mind.

Leaving the mix with butter lumps will lead to spongy, cake-y cookies. :(

I have been baking this recepie for years! There is a post on there that tells you to increase the baking soda to 2 tsp. (I cut the recipe down to 36 cookies too) and 2 Tablespoons (yes tablespoons) vanilla. I bake at 330 for 12 min. They turn out amazing!!

I know I’m years late, but this is also for other people having the same problem. If this is happening despite the correct temperature, time, ingredients, and instructions, it’s probably your oven. Same thing happened to me literally thirty minutes ago. My oven only heats from the bottom, whereas an other oven would have heat surging around the cookie, not just the bottom. I recommend (if you don’t want to buy an oven with the “turbo” option) baking in a toaster with the turbo mode.