Preheat the oven to 350° and line 2 large baking sheets with parchment paper.

In a large mixing bowl, whisk together flour, cocoa powder, baking powder and salt.

In the bowl of a stand mixer (a hand mixer also works), beat together apple sauce and sugars until smooth.

Heat a pot of water over the stove and place a bowl on top to create a double boiler. Add the chocolate and vegan butter and heat, stirring occasionally, until completely melted.

With the mixer running on low speed, slowly add the chocolate mixture until well incorporated then use a spatula to fold in the dry ingredients. The batter will be very loose.

Use a small cookie scoop (about 2 tbsp) to portion out the batter onto the baking sheet. Leave a couple inches in between each cookie. Allow the batter to sit on the baking sheet for 5-10 minutes or until firm. Use your hands to roll into balls and place back on the baking sheet.

Bake for 17 minutes. Let the cookies cool for 15 minutes on the sheet pan then transfer to a wire rack to cool completely before frosting.

Add the softened vegan butter and tahini to the bowl of a stand mixer. Beat until light and fluffy.

Add the vanilla extract and 1 cup of powdered sugar. Beat until smooth, adding 1/2 cup more powdered sugar at a time until the frosting has thickened.

Use a piping bag or spatula to spread frosting onto the flat side of one cooled cookie and place another on top to make a sandwich. Garnish with flaky salt if desired and serve at room temperature.