Line a baking sheet with parchment paper and preheat your oven to 350 F (175 C).
Melt the butter in a small saucepan over medium heat. Let it cook until it becomes very bubbly, then stir it frequently as the bubbles begin to subside and the butter develops a brown, caramel-like colour.
Allow the butter to cool for 10 minutes before adding the remaining ingredients.
Using either a hand-held mixer or a spatula, cream together the butter, granulated sugar and light brown sugar.
Add in the eggs, vanilla extract and lemon extract and mix well.
In a separate bowl, combine the flour, rolled oats, cinnamon, salt and baking soda.
Add the flour mixture to the butter mixture and using your hand-held mixer on low speed, combine.
Fold in the blueberries.
Use a cookie scoop and portion out your cookie batter onto the parchment paper leaving each cookie about 1/2 inch apart.
Bake for 13 -15 minutes or until the cookies are golden brown on the top.
Remove the cookies from the oven and allow to cool for five minutes before transferring them to a cooling rack.
For the icing, use a handheld mixer to combine the icing sugar, lemon and vanilla extract and milk until smooth.
Once the cookies have fully cooled, drizzle over the lemon icing.