Prep: Line a baking sheet with parchment paper. Also, line a cutting board with a small sheet of parchment paper for the cookie dough balls. Set aside.
Mix dry ingredients: In a medium bowl, stir together flour, baking powder, baking soda, and salt. Set aside.
Cream butter and sugars: In a large mixing bowl, use an electric hand mixer to beat the softened butter on medium speed until it becomes very creamy and pale in colour. Add the granulated sugar and brown sugar and beat together until fluffy.
Add egg: Add the egg and mix until combined.
Add wet ingredients - Add the peanut butter, miso paste, and vanilla extract and beat again until combined.
Add dry to wet mixture: Add the flour mixture to the butter mixture. Mix on low speed until almost combined. Finish mixing the dough with a spatula to prevent overmixing.
Scoop cookie dough: Use a 4-tablespoon scooper to scoop out balls of cookie dough. Release them onto your lined cutting board.
Chill: Place the whole board with the cookie dough balls into the fridge and chill for about 15 minutes, just until they are firm enough to pick up. In the meantime, preheat the oven to 350°F.
Coat in sugar: Fill a small bowl with sugar crystals. Roll each cookie dough ball in the sugar crystals until generously coated on all sides.
Flatten: Place the cookie dough on your lined baking sheet, leaving about 2" in between each cookie. Use the back of a fork to press down on each dough ball to flatten slightly and create a crosshatch pattern.
Bake: Bake cookies for 12-13 minutes or until the bottom edges just barely start to brown and the cookies are still very soft. Let the cookies cool on the baking sheet for at least 15 minutes to set. Transfer the cookies to a wire rack to cool completely or enjoy some warm!