Blueberry Muffin Cookies with Streusel Topping: A Sweet, Fluffy Delight

In a small bowl, combine the flour, sugar, cinnamon, and salt. Add the cold cubed butter and use a pastry cutter or your fingers to blend the mixture until it resembles coarse crumbs. Set aside.
Make the Cookie Dough:

Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.
In a medium bowl, whisk together the flour, baking soda, baking powder, and salt.
In a separate large bowl, cream together the softened butter and granulated sugar until light and fluffy (about 2-3 minutes). Add the egg and vanilla extract, beating until combined. Mix in the sour cream or yogurt until smooth.
Gradually add the dry ingredients to the wet ingredients, mixing until just combined.
In a small bowl, toss the blueberries with cornstarch to coat them lightly. Gently fold the blueberries into the cookie dough, being careful not to crush them.
Assemble the Cookies:

Drop spoonfuls of the cookie dough onto the prepared baking sheet, spacing them about 2 inches apart.
Sprinkle a generous amount of the streusel topping over each cookie dough mound.
Bake the Cookies:

Bake the cookies in the preheated oven for 12-15 minutes, or until the edges are lightly golden and the streusel is crisp. The cookies will firm up as they cool.
Allow the cookies to cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely.
Serving and Storage Tips: