Place the vegan butter and granulated sugar in the bowl of a stand mixer and cream them together on medium speed until smooth and fluffy (2-5 minutes).
Add the apple sauce and vanilla bean paste and beat again until smooth.
In a separate small bowl, combine the flour, cream of tartar, bicarbonate of soda, and fine sea salt. Add to the stand mixer bowl and beat on slow until just combined.
Remove the dough from the mixer bowl and weigh it. Divide the dough in half and separate into two bowls. Cover one bowl with reusable plastic wrap and place in the fridge. Add the espresso powder and the cocoa to the other half of the dough and mix until combined. Cover and place in the fridge for 30 minutes.
While the dough cools, preheat the oven to 170c/340f (fan) and line two baking sheets with baking parchment. Place granulated sugar for rolling in a shallow bowl and set aside.
Once the dough is cooled, remove both bowls from the fridge. Starting with the vanilla dough, divide it into 12 equal sized portions and form into rough balls with your hands. Set aside. Wash your hands and repeat the process with the espresso dough.
Gently squeeze together an espresso and vanilla ball together and roll them into one ball in your hands. Drop into the sugar and roll to coat all over. Remove from the sugar and place on the lined baking tray. Repeat the process until you have 12 combined balls of dough spread across the two baking trays.
Place one tray with six balls of dough into the oven and bake for 10-12 minutes. The dough will spread and crisp up around the edges slightly but will still look slightly under-done in the centre. Don't worry - this is correct and will help the cookies to stay soft and chewy in the centre. Remove the cookies and repeat with the second tray while the others cool.
Allow the cookies to cool for at least 20 minutes before serving.