Beat 1 cup unsalted butter, 3/4 cup brown sugar1/2 cup granulated sugar together on medium-high until light and fluffy, about 2–3 minutes.
1 cup unsalted butter, 3/4 cup brown sugar, 1/2 cup granulated sugar
Add 2 large eggs one at a time, beating well after each, then mix in 2 tsp vanilla extract until smooth.
2 large eggs, 2 tsp vanilla extract
In a separate bowl, whisk 1 1/2 cups all-purpose flour, 1 tsp baking soda, and 1/2 tsp salt. Add to the wet ingredients and mix on low just until no dry streaks remain. Stir in 3 cups old-fashioned rolled oats until evenly distributed, then fold in 1 cups white chocolate chips.
1 1/2 cups all-purpose flour, 1 tsp baking soda, 1/2 tsp salt, 3 cups old-fashioned rolled oats, 1 cups white chocolate chips
In a small bowl, toss 3/4 cup frozen blueberries with 2 tbsp all-purpose flour until lightly coated, working quickly so they stay frozen. Fold them into the dough with just a few gentle strokes.
3/4 cup frozen blueberries, 2 tbsp all-purpose flour
Cover the dough and chill in the refrigerator for at least 45 minutes. Preheat the oven to 350°.
Scoop 2 tbsp mounds onto two parchment paper lined sheets, spacing them about 2 inches apart. Bake for 12–13 minutes, until the edges are golden but the centers still look slightly underdone.
Let the cookies rest on the sheet for 5 minutes to finish setting, then transfer to a wire rack to cool.