In a skillet over medium heat, melt the butter, stirring as it foams, turns amber, and brown solids form at the bottom. Once golden and fragrant, remove from heat. Transfer to a bowl and cool for 20 minutes.

**Tip: Butter should be room temperature; if still warm, chill in the freezer for 10 minutes to prevent excess cookie spreading.

In a bowl, sift together flour, cornstarch, baking soda, baking powder, and salt. Set aside.

In a large bowl, combine the cooled brown butter, granulated sugar, and brown sugar. Stir until smooth, then mix in eggs and vanilla.

Gradually fold dry ingredients into the wet mixture until just combined.

Wrap dough in plastic wrap and refrigerate for at least 1 hour.

While dough chills, combine blueberries, sugar, and lemon juice in a saucepan. Cook on medium, stirring, until thickened, about 30 minutes. Set aside.

Preheat oven to 350°F (175°C). Line a baking sheet with parchment. Scoop 3 oz balls of dough, placing them 2 inches apart. Bake for 12 minutes, until edges are golden and centers soft.