Preheat the oven to 350F then line a baking sheet with parchement paper and set it aside.
In a stand mixer bowl, cream the butter, and brown sugar together until smooth. Add in the egg, molasses, and vanilla and mix again to combine.
Mix in the oats, flour, cinnamon, corn starch, baking powder, and salt just until the dry mixture disappears. Save about 1 tablespoon of cookie dough aside.
Using a large cookie scooper, scoop out 7 equally sized cookie dough balls, place them on the prepared baking sheet and gently press down with the back of a ¼ cup measuring cup. Bake in the preheated oven for 12 minutes. Once the cookies come out, press the center with a measuring cup again in case you lost that well in the center.
In a small parchement lined baking sheet crumble the 1 tablespoon of cookie dough and bake in the oven for 6 minutes. Pull out the cookie dough, let it cool down for a few minutes then crumble it some more and bake again for 2 minutes to get it extra crunchy.