Mix flaxseed meal and water in a small bowl; let it sit for 5 minutes.
In a large bowl, whisk flour, baking soda, and sea salt.
In a second bowl, cream vegan butter, brown sugar, and white sugar until light and fluffy.
Add the flax egg and vanilla. Mix until smooth.
Combine wet and dry mixtures until just combined. Stir in chocolate chips.
Chill dough for 10 minutes (yes, it needs a break too).
In another bowl, beat vegan butter until smooth.
Add powdered sugar, coffee, vanilla, and milk. Beat until fluffy and creamy.
Scoop 1 tbsp cookie dough, flatten, and place ½ tsp buttercream in the center.
Cover with another bit of dough and seal edges. Repeat like a fabulous cookie factory.
Place cookies on parchment-lined tray and bake at 350°F (175°C) for 12 minutes.
Cool for 10 minutes before attacking them like a woman possessed.