In a large mixing bowl, add your flour, baking powder, and baking soda and mix well. Set aside. In a separate bowl, whisk together your powdered sugar, peanut butter, and milk, until thick and smooth.
Combine your wet and dry ingredients. If the dough is too thick, add an extra tablespoon of milk. If you want thicker cookies, cover the mixing bowl and refrigerate the cookie dough for 30 minutes.
Preheat the oven to 180C/350F. Line a large baking tray with parchment or a cookie sheet.
Remove the cookie dough from the refrigerator and form 12 balls of dough. Place each ball of cookie dough on the lined tray, one to two inches apart. Press down on each cookie or use a cookie stamp. Bake the cookies for 10-12 minutes, or until just beginning to go golden.
Remove from the oven and allow cookies to cool on the tray completely.
Notes
TO MAKE AHEAD COOKIE DOUGH- If you'd like to prepare the dough in advance, you can keep it chilled and covered for up to 2 days. Be sure to remove it from the refrigerator 30 minutes before baking. TO STORE- Leftover cookies will keep fresh at room temperature, in a sealed container, for up to 2 weeks. They will keep longer if you refrigerate them. TO FREEZE COOKIES- Place cookies in a ziplock bag and place it in the freezer for up to 6 months. TO FREEZE COOKIE DOUGH- Form a large ball of cookie dough and wrap in plastic wrap, ensuring no pockets of air can enter, and it is completely sealed. Place in the freezer for up to 2 months. Before using the cookie dough, thaw it overnight in the refrigerator, before letting it sit at room temperature for 30 minutes, before baking.