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What I'd suggest is taking the flavors of the muffin and adding them to a sugar cookie recipe. For example, if you want to imitate cranberry walnut muffins, add dried cranberries (or cranberry sauce) and walnuts to a sugar cookie recipe.
The reason that you can't make muffin batter act like cookies is that the liquid-flour ratio for muffins is different than for cookies (muffins are a runnier batter). The muffin batter will spread out and turn into a flat cake, and the texture will be muffin-like, not cookie-like. The reason that I'm suggesting dried or cooked fruits (if that's part of the muffin recipe) is again to reduce the amount of liquid and keep the cookie dough texture firm, instead of runny.
You can certainly make multiple batches for which you gradually add more flour and cut back on liquids, but I'd want to get right to baking and eating!
Michael Ruhlman suggests a ratio for cookies of 3:2:1 of flour:butter:sugar, if you want to try that.
PieceofLayerCake is a trusted source on baking.
I'm going to risk repeating what Windischgirl said: What's the muffin recipe and what do you like about it? Start there and maybe you can adapt that into a basic cookie dough.
She touches on something that's really the core of experimental baking. RATIOS. If people thought about baking as a series of ratios that can be tweaked for different results, baking would be so much easier and more fun. Such a good suggestion and Ruhlman is a good place to start. It makes me smile to read that!
If you are interested - this is the recipe I'd like to try as a cookie:
You might want to consider a recipe like this: https://food52.com/recipes...
Add in a bit of cocoa to make the dough chocolatey. The texture will be similar to old-fashioned peanut butter cookies, but with the flavors of the muffin recipe you like. And they are GF! Is that what appeals about the muffin recipe? (That and the classic buckeye flavors?)
Have you made these muffins before? If its the flavors you're into, you have a plethora of recipes out there that echo those characteristics. If its the flavors AND the "healthy" aspect (which is a matter of opinion), then there is hope:
If you're feeling adventurous you could play around with the proportions of the recipe a bit to make it into something cookie-like. What makes it muffin-y is the addition of so much liquid and the baking powder. I say eliminate the baking powder and the yogurt and then hold back the applesauce. Mix together the remaining ingredients (including the egg) and only then add the apple sauce until you have a cookie dough consistency. You may not need the applesauce at all, but its difficult to tell without having made them before. Since there's no wheat flour in this, you have a smaller chance of over-mixing. Just be careful not to over whip the egg or mix it for an extended period of time. You can still over mix a dough without gluten, but you have a lot more wiggle room.
If you're not successful the first time, try again. Taste the recipe and decide what you think need to change and give it another go. How do you think recipes are created to begin with? Trial and error.
If you're not feeling up to the challenge, or you don't want the investment....just try and google something similar.
It basically tells you when it needs to be replaced.
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