Step 1: Prepare the Blueberry Swirl

Combine Ingredients: In a small saucepan, combine the blueberries, granulated sugar, cornstarch, and water.

Cook and Thicken: Place the saucepan over medium heat, stirring occasionally to prevent sticking. Cook for approximately 5 minutes, or until the mixture thickens to a jam-like consistency. The cornstarch will help create a smooth, glossy sauce.

Mash and Cool: Once thickened, remove the saucepan from the heat. Gently mash the blueberries with a fork or potato masher to release their juices and create a more uniform texture. Allow the blueberry swirl to cool completely while you prepare the other components. This step is crucial to prevent the swirl from melting and spreading too much during baking.

Step 2: Make the Cheesecake Filling

Cream the Cream Cheese: In a small bowl, add the softened cream cheese. Using an electric mixer (handheld or stand mixer), beat the cream cheese until it is smooth and creamy. It's vital that the cream cheese is at room temperature to avoid any lumps in the filling.

Add Sugar and Vanilla: Gradually add the granulated sugar to the cream cheese, continuing to beat until the sugar is fully incorporated and the mixture is light and fluffy. Then, add the vanilla extract and mix until well combined. Set the cheesecake filling aside.

Step 3: Prepare the Cookie Dough

Cream Butter and Sugars: In a large bowl, cream together the softened butter, granulated sugar, and packed light brown sugar. Use an electric mixer to beat the mixture until it is light and fluffy. This process, known as creaming, incorporates air into the butter and sugar, which is essential for creating a tender cookie.

Add Egg and Vanilla: Add the large egg and vanilla extract to the creamed butter and sugar mixture. Mix until everything is well combined. Be sure to scrape down the sides of the bowl to ensure all ingredients are evenly incorporated.

Combine Dry Ingredients: In a separate bowl, whisk together the all-purpose flour, baking soda, and salt. Whisking ensures that the baking soda and salt are evenly distributed throughout the flour.

Gradually Add Dry Ingredients to Wet Ingredients: Gradually add the dry ingredients to the wet ingredients, mixing on low speed until just combined. Be careful not to overmix the dough, as this can result in tough cookies. Mix until you just see a cohesive dough forming.

Step 4: Assemble the Cookies

Preheat Oven and Prepare Baking Sheet: Preheat your oven to 350°F (175°C). Line a baking sheet with parchment paper. Parchment paper prevents the cookies from sticking and makes cleanup a breeze.

Scoop Cookie Dough: Using a cookie scoop or a spoon, scoop 2-tablespoon-sized portions of dough onto the prepared baking sheet, spacing them about 2 inches apart.

Create Wells: Use your thumb or the back of a spoon to gently press a small well into the center of each dough ball. This well will hold the cheesecake filling and blueberry swirl.

Add Fillings: Spoon a small amount of the cheesecake filling (about 1 teaspoon) into each well, followed by a small dollop of the cooled blueberry swirl (about ½ teaspoon).

Swirl the Fillings: Use a toothpick or a thin knife to gently swirl the cheesecake filling and blueberry swirl together, creating a marbled effect. Be careful not to over-swirl, as this can cause the colors to blend too much.

Step 5: Bake the Cookies

Bake: Place the baking sheet in the preheated oven and bake for 12-15 minutes, or until the edges of the cookies are set and the centers are slightly soft. The cookies should be lightly golden brown around the edges.

Cool: Remove the baking sheet from the oven and let the cookies cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely. This allows the cookies to firm up slightly, preventing them from breaking when you move them.