Weigh or measure the white and dark brown sugars into a small bowl and set aside. In another bowl, weigh or measure the flour, baking powder, salt, and old-fashioned oats. Whisk to blend.
Add the cubed butter to the mixer bowl. Gradually increase to medium speed and cream the butter for 1-2 minutes.
Add both sugars and mix on medium speed for 3 minutes.
Add the egg and vanilla bean paste and mix until incorporated. Stop and scrape down the sides and bottom of the bowl.
On low mixer speed, gradually add the flour and oat mixture. Mix just until the dry ingredients are incorporated. The cookie dough will be thick.
Add the dried blueberries, cinnamon chips, and chopped walnuts. Mix just until evenly distributed throughout the dough. Cover and chill for about 15 minutes.
Preheat the oven to 350°F (175°C or 180°C) and line 2 cookie sheet pans with parchment paper. Using a medium cookie scoop, place 12 mounds of dough onto one prepared pan, keeping the bottoms as flat as possible.
Cut a small square of parchment paper and place it over a mound of cookie dough. Using a small, flat-bottomed glass, gently press the mound to about ½ inch thick. Repeat with the remaining cookie dough.
Bake for 11-13 minutes. The tops will still look a little underdone, but the cookies will firm up as they cool.
Leave the cookies on the sheet pan for 1-2 minutes before moving them to a cooling rack.