Preheat oven to 350°F (177°C). Line a large baking sheet with parchment paper.
In a large microwave-safe mixing bowl, add chocolate chips. Heat in microwave in 15-30 second intervals, stirring in between with a spatula, until chocolate is melted and smooth. You can also melt the chocolate on the stove using the double boiler method.
Add in the cornstarch. Stir it in until the cornstarch is completely and evenly incorporated into the batter. Make sure you don't have any streaks of melted chocolate that haven't been mixed with the cornstarch. Your batter should be uniform in color and have the consistency of a chocolate spread (like Nutella).
Add chocolate batter to a piping bag. Using a large open star tip (I used one with a 1/2 inch opening), pipe chocolate swirls or whatever design you prefer. See notes for other options if you don't wish to pipe the cookies.
Bake cookies for about 6 minutes. The cookies should look dry and done on the surface. Do not touch the cookies to check if they are done because they will be extremely hot when they come out of the oven. Let the cookies cool before eating. If you don't mind your hands getting a little melted chocolate on them, the cookies taste best right after they are cooled (about 30-60 minutes after they are done) but the surface of the cookies will be a little sticky. If you let the cookies cool for several hours, they will no longer be sticky on the surface but the texture of the cookies will be much firmer. You can enjoy them fully cooled but you can also warm them up briefly to soften the texture. See notes for more details.
Notes
I only pipe these cookies when I plan on gifting them. If I am just making them for myself then I just make plain round cookies. I use a 2 tsp cookie scoop and scoop the batter. Then I use the back of a metal spoon to flatten the cookies to thick round disks. (I then wet the back of the spoon slightly so that I can smooth the surface of the cookies). Making the cookies this way is much easier and you don't lose as much batter (I am able to make 1-2 more cookies).
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These cookies don't have the exact same texture as classic butter cookies, but they are very similar. If you eat them soon after they are baked, the texture will be almost exactly the same as classic butter cookies (slightly crispy and crunchy on the outside and crumbly and melty in your mouth). Once the cookies cool for several hours, they do get much firmer (like biting into a chocolate bar). When you first bite in, you might think the cookies are almost hard but then they will quickly melt in your mouth. If you don't like the firmness, you can easily soften them again by warming them up in the microwave for a few seconds (10-15). When I gift them, I write instructions to warm them up before eating.
I recommend lining your cookie sheet with parchment paper and not a silicone baking mat because if you use a silicone baking mat, the bottom of your cookies will have grid imprints from the silicone mat.
The nutrition information provided are only estimates based on an online nutritional calculator. This is not a comprehensive list of all the nutrients in the recipe (i.e., does not include vitamins, cholesterol, etc). I am not a certified nutritionist. Please consult a nutritionist or doctor for accurate information and any dietary restrictions and concerns you may have.