Preheat the oven to 350 degrees. Line 2 baking sheets with parchment paper.In a large bowl, cream together the butter, peanut butter, maple syrup, and vanilla until smooth. Add the flour and baking powder, beat until combined and the dough begins to form a ball. If the dough is crumbly, add 2-3 teaspoons water. If the dough feels moist, add 1-2 tablespoons flour. Roll the dough into tablespoon size balls. Cut each ball in half, press the 2 balls together, and place them on the prepared baking sheet. Gently flatten each cookie. Using a fork, create a crosshatch pattern (see above photos). Transfer to the oven and bake for 9-10 minutes.To make the filling, beat together the peanut butter, butter, and maple syrup until combined. Spread an even layer on one cookie and sandwich another on top.To make dipping easier, freeze the cookies for 10 minutes. Then drizzle or dip the cookies into chocolate. Sprinkle with salt if desired. Eat...or let the chocolate harden and store in an airtight container for up to 5 days. Enjoy!