Start by cutting cold unsalted butter into small cubes, then combine it in a mixing bowl with all-purpose flour, brown sugar, ground cinnamon, and a pinch of salt. Use your fingers or a pastry cutter to mix until the mixture resembles coarse crumbs. Once combined, refrigerate the streusel while you prepare the rest of the Coffee Cake Cookies dough.

In a medium bowl, sift together all-purpose flour, baking soda, ground cinnamon, and salt to ensure even distribution. This step is essential for creating a light texture in your Coffee Cake Cookies. Set the bowl aside.

In a large mixing bowl, beat the softened unsalted butter with granulated sugar and light brown sugar using an electric mixer on medium speed for 2-3 minutes until the mixture turns light and fluffy.

With the mixer still on low, add in the eggs—both whole and yolk—along with the vanilla extract, one at a time. Beat each addition until smooth and fully combined, which should take about 2 minutes.

Gradually add the dry ingredients you set aside earlier to the wet mixture. Use a spatula or wooden spoon to gently fold them together until just combined.

Using a 2 oz cookie scoop, portion the dough onto lined baking sheets, spacing them about 2 inches apart. Create a small indent in the center of each cookie with your finger or the back of a spoon.

Cover the baking sheets with plastic wrap or a clean kitchen towel and refrigerate the shaped cookie dough for at least 1-2 hours.

Preheat your oven to 350°F (180°C). Once ready, take the cookie dough out of the fridge and generously top each cookie with the chilled streusel mixture. Bake for 13-15 minutes.

Remove the cookies from the oven and allow them to cool on the baking sheets for about 5 minutes before transferring them to wire racks. Mix powdered sugar, whole milk, and vanilla extract to create a smooth icing. Drizzle the icing over the cookies.