In a medium bowl, whisk together the flour, cinnamon, nutmeg, baking soda and salt. Set aside.
In a large bowl, beat together the butter, brown sugar and granulated sugar until creamed (about 2 minutes).
Beat the egg and vanilla into the butter mixture.
Starting with the mixer on a low speed, beat the flour mixture into the butter mixture until combined.
Mix in the oats. You can do this either by hand or with the mixer on a low speed.
Very carefully, stir in the blueberries using a rubber spatula or wooden spoon. Be careful not to squish or pierce the berries.
Cover the bowl with plastic wrap and refrigerate for 30 minutes.
When ready to bake, preheat the oven to 350F (180C) and line cookie sheets with parchment paper.
If your dough has been in the fridge for over 2 hours, let it sit on the counter for 10-15 minutes to warm up slightly first. Form the dough into balls with about 2 to 2.5 tablespoons of dough each. Again, be very careful not to pierce the berries. Place the dough balls about 2 inches apart on the lined cookie sheets.
Bake 1 sheet at a time in the middle of the oven for about 13-15 minutes, or until the tops look just set.
Cool the cookies on the cookie sheet for at least 10 minutes before transferring to a cooling rack to continue cooling.