Preheat your oven to 350°F (175°C). Line your baking sheet with parchment. Be better than your last baking attempt.
In a small bowl, combine flaxseed and water. Let it thicken like your skincare routine.
Mix flour, baking soda, salt, and espresso powder in a separate bowl.
In another bowl, beat vegan butter, brown sugar, and cane sugar until fluffy.
Add flax egg and vanilla to the butter mixture. Whip it good.
Stir dry ingredients into wet. Fold in chocolate chips with flair.
Scoop tablespoon-sized dough balls onto the baking sheet. Flatten slightly with the back of a spoon.
Bake 11–12 minutes until edges are golden and center still soft. Let cool completely.
For filling, beat vegan butter, powdered sugar, vanilla, espresso, salt, and milk until smooth and creamy.
Match up cookies in pairs. Spread filling on one side, top with another. Repeat until your willpower breaks.