Combine the water, fresh blueberries, granulated sugar, lemon juice, a pinch of salt, and cornstarch in a saucepan over medium heat. Stir gently until the mixture becomes bubbly, and the blueberries begin to soften.

Cook until it thickens slightly to add sweetness and fruitiness to the cookies.

Melt the salted butter in a saucepan over medium heat, stirring constantly until it turns golden brown. Let it cool slightly before adding to the mixing bowl.

In your mixing bowl, combine the light brown sugar and granulated sugar with the browned butter. Blend together until smooth.

Add the large egg and egg yolk along with the vanilla extract. Mix until well combined.

Whisk together the all-purpose flour, baking powder, salt, and cinnamon in another bowl. Gradually add to the wet ingredients, mixing just until dough comes together.

Fold in the fresh blueberries gently.

Stir in the blueberry jam for moisture and sweetness.

Preheat oven to 350°F. In a small bowl, mix light brown sugar, all-purpose flour, cinnamon, and salt. Cut in cold salted butter until the mixture resembles coarse crumbs.

Scoop out portions of dough onto a baking sheet lined with parchment paper, leaving space for spreading.

Sprinkle the cinnamon streusel over each cookie dough mound.

Bake in preheated oven until lightly golden around the edges, keeping a close watch towards the end.