Step 1

Preheat oven to 350°. Toast pecans on a rimmed baking sheet, tossing once, until fragrant and slightly darkened, 10–15 minutes; let cool. Pulse pecans in a food processor until the consistency of coarse meal. Add flour, sugar, salt, and cinnamon and pulse just to combine. Add butter and pulse until mixture resembles coarse meal with a few pea-size pieces remaining.

Step 2

Transfer to a large bowl; drizzle with 4 Tbsp. ice water and mix, adding another tablespoonful of water if needed, just until mixture comes together. Gently pat dough into a 6"-diameter disk. Wrap in plastic and chill at least 1 hour.

Step 3

Do Ahead: Dough can be made 2 days ahead. Keep chilled, or freeze up to 1 month.

Step 4

Preheat oven to 375°. Toss blueberries, cornstarch, lemon juice, and ¼ cup sugar in a large bowl.

Step 5

Roll out dough on a lightly floured surface to a 12" round. Carefully transfer to a parchment-lined baking sheet. Mound blueberries in center of dough, leaving a 2" border. Fold edges over, overlapping slightly. Brush dough with milk and sprinkle with sugar.

Step 6

Bake galette until crust is dark golden brown and filling is bubbling, 45–50 minutes. Let cool before serving.

Step 7

Do Ahead: Galette can be baked 1 day ahead. Store tightly wrapped at room temperature.