Preheat oven to 350°F (175°C). Line baking tray with parchment.
Mix flaxseed and water in a small bowl. Let it thicken like your latest situationship.
In a large bowl, whisk peanut butter, sugar, maple syrup, and vanilla until smooth.
Stir in flax egg, baking soda, salt, and flour. Mix until dough forms.
Roll dough into 24 small balls, then gently flatten. Place on tray.
Bake for 10 minutes. Let cool before adding cream or chaos may ensue.
For the filling, beat vegan butter until fluffy. Add powdered sugar, espresso, plant milk, and vanilla. Whip until smooth.
Spoon or pipe filling on 12 cookies. Sandwich with the other 12.
Devour responsibly or irrationally—your call.