Add the blueberries, sugar, lemon juice, vanilla and cornstarch to a small pot.

Cook over medium-low heat for 25-30 minutes until the blueberries are very thick and measure out to a ¼ cup (60 ml). About 8 minutes in, smush some of the blueberries with the back of a wooden spoon. Stir a lot towards the end so it doesn’t stick to the bottom of the pot.

Transfer to a small bowl and allow to completely cool. Cover with plastic wrap so a skin doesn't form on the jam.

Add the butter and brown sugar to a medium bowl. Mix together with an electric mixer on high speed until combined.

Add in the flour and salt and mix together until the mixture resembles large crumbs.

Chill the streusel for 30 minutes in the fridge while working on the dough.

Preheat the oven to 350 ℉ (175 ℃). Line 2 baking sheets with parchment paper and set aside.

In a large bowl, whisk together the flour, baking powder and salt. Then set aside the flour mixture.

In a large mixing bowl cream together the softened butter and granulated white sugar with an electric mixer on high speed until fluffy, about two minutes.

Add in the egg and vanilla and mix on medium speed until pale in color and fluffy, 1-2 minutes.

Slowly add in the dry ingredients to the wet ingredients. Mix on low speed just until the dough pulls together. Scrape the sides of the bowl with a spatula as necessary.

Push some of the dough to the sides of the bowl to create a large space. Add in the blueberries.

Gently fold the blueberries into the dough with a rubber spatula.

Create little holes in the dough with a spoon and add half the jam into the holes. Gently fold the jam in, but do not mix it in all the way.

Flatten the dough with a rubber spatula. Make little holes again and add in the rest of the jam to the created holes. Gently fold the jam again, being careful not to mix it in all the way.

Scoop the dough with a 2 tablespoon cookie scoop. Use a tablespoon to create a little indent in each scoop of dough.

Measure out a slightly packed, heaping tablespoon of streusel topping and flip it on top of each portion of cookie dough. Press down gently with your fingers to secure the streusel to the cookie dough.

Bake the cookies for 12 minutes, then remove them from the oven and quickly scoot a circular cookie cutter or glass, that is just slightly larger than the cookies, around each to push the cookies into a perfect circle.

Then return the cookies to the oven and bake for an additional 2 minutes.

Let the cookies cool on the baking sheet for at least 10 minutes.

While the cookies cool, mix together the powdered sugar and milk in a small bowl. Start with 3 teaspoon of milk and add more as necessary.

Once the cookies are cooled, drizzle the icing over each cookie. Then enjoy!