Melt the butter in a medium saucepan. Once melted, whisk in the brown sugar. Bring to a boil over high heat and cook 1 minute. Remove from the heat and transfer to a bowl. Whisk in the vanilla. Add the almond flour and salt mixing until combined. Let cool 5 minutes, then stir in the egg white. Let the dough sit 10 minutes to thicken. Position racks in the upper and lower thirds of the oven. Preheat the oven to 350 degrees F. Line 2 baking sheets with parchment paper.Drop 1 teaspoons size amounts of dough on prepared baking sheet, placing each 3 inches apart. Bake for 7-9 minutes until golden brown around the edges. The butter will be bubbling up around the cookies, this is OK. Allow the cookies to cool on the baking sheet for 5 minutes, then transfer to a wire rack to cook completely. To make the filling. Combine chocolate and cream microwave-safe bowl and microwave, stirring every 45 seconds, until melted. Stir in the vanilla and coffee powder. Let cool 10 minutes, until slightly thickened and spreadable. Sandwich each cookie with the chocolate filling or melted milk chocolate. Store cookies in an airtight container for up to 4 days.