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.
2 1/2 cups (313 g) all-purpose flour, spooned and leveled, 1/2 tsp baking powder, 1/2 tsp salt
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. (You can also use the bowl of a stand mixer fit with a paddle attachment.) 1 cup (224 g) unsalted butter, softened, 1 1/4 cups (250 g) granulated white sugar
Add in the egg and vanilla and mix on medium speed until pale in color and fluffy, 1-2 minutes.
1 egg, at room temperature, 1 tbsp vanilla
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. 8 oz (226 g) fresh blueberries
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. (I like to fold each quarter section once, then fold all the dough over on itself once.) jam from above
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 tbsp 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. Add any pieces of streusel that fall off back on top.
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 and thicken them up a bit from the spreading in the oven. Then return the cookies to the oven and bake for an additional 2 minutes.
Very important- let the cookies cool on the baking sheet for at least 10 minutes. They will continue baking as they cool and firm up. Because these cookies are full of fresh blueberries and jam, a few extra steps are needed to make sure they come out perfectly! :) Then transfer the cookies to a cooling rack to finish cooling.