Preheat the oven to 175 ºC (350ºF). Line a couple of sheet pans with parchment paper.
Place the blueberries on a parchment-lined rimmed baking sheet and freeze while you make the cookie dough.
In a medium bowl, whisk together the flour, oats, baking soda, salt, and fresh rosemary. Set aside.
In a large bowl, cream together the butter with the two sugars until they are well mixed with a wooden spoon (or in the mixer if you prefer).
In a small cup, whisk together the egg, vanilla, and maple syrup.
Drop this mixture into the bowl with the creamed butter, a little at a time, stirring well with each addition.
When the egg mixture has been incorporated, pour the dry ingredients into the bowl. Stir to combine.
Dump in the white chocolate chunks and the frozen blueberries, folding them in carefully.
Scoop heaped tablespoons of the cookie dough onto a big parchment-lined sheet. Chill the cookies for 15 minutes.
Bake the cookies for 12 to 16 minutes in the oven or until the edges are beginning to brown. Note the baking time is entirely dependent on your oven and how cold the cookie dough is.
Let cool before transferring to a rack. I stored these on the wire rack, uncovered, overnight, so that the cookies dried out a little. The next day you will have perfectly chewy blueberry cookies, whereas fresh from the oven, they were a little moist and cakey.