Combine the flax meal with three tablespoons of warm water. Mix it and set it aside for five minutes, to gel (this is a “flax egg”).
In the meantime, place the butter and sugars in a stand mixer fitted with the paddle attachment. Beat them on medium speed for 3-4 minutes, till fluffy. Add the flax egg and the vanilla extract. Continue to beat for one more minute.
Add the flour, cornstarch, salt, baking powder, cinnamon, and oats to the stand mixer. Mix on low speed for about 30 seconds, or until the ingredients are mixed evenly. Add the raisins and mix again to incorporate. The cookie dough will be somewhat wet. Transfer the dough to the fridge for at least 1 hour and up to overnight.
Preheat your oven to 350F and line a baking sheet with parchment paper. Drop the cookie dough by two-tablespoon heaps onto the baking sheet. Space the cookies two inches apart.
Bake the cookies for 12-14 minutes, or until they’re just browning at the edges. Allow them to cool on their sheets for five minutes, then use a large spatula to transfer them gently to a cooling rack to cool completely. Enjoy or store.