Step 1: Prepare the dough

• Mix dry ingredients: In a medium-sized bowl, whisk together the flour, baking soda, and salt. Set aside.
• Cream the butter and sugar: In a large bowl, use a hand mixer or stand mixer to cream together the softened butter and sugar until light and fluffy. This will take about 2-3 minutes.
• Add egg and vanilla: Beat in the egg and vanilla extract until fully incorporated.
• Add sour cream: Stir in the sour cream, which will keep the dough soft and tender. Mix until smooth.
• Combine with dry ingredients: Gradually add the dry ingredients into the wet ingredients, mixing just until combined. Be careful not to overmix, as this can lead to tough cookies.

Step 2: Make the cinnamon filling

• Melt the butter: In a small bowl, melt the butter in the microwave or on the stovetop.
• Mix cinnamon and sugar: Stir together the brown sugar and cinnamon in another bowl.
• Combine: Once the butter is melted, mix it with the cinnamon-sugar mixture. Set this filling aside.

Step 3: Roll out the dough

• Chill the dough: Divide the dough into two portions and wrap them in plastic wrap. Chill in the fridge for at least 30 minutes. This helps the dough firm up and makes it easier to roll out.
• Roll out the dough: Once the dough is chilled, place one portion on a floured surface and roll it out into a rectangle about 1/4-inch thick.
• Spread the cinnamon filling: Brush the melted cinnamon-sugar butter mixture over the rolled-out dough, spreading it evenly all over. Leave a small border around the edges.

Step 4: Shape the cookies

• Roll up the dough: Starting from one of the long sides, carefully roll the dough into a log. Be gentle to prevent the filling from spilling out.
• Slice the dough: Using a sharp knife, slice the dough into 12 equal pieces. These will form your cookies.
• Place on a baking sheet: Arrange the cookie slices on a baking sheet lined with parchment paper or a silicone baking mat. Make sure to space them out evenly.

Step 5: Bake the cookies

• Preheat the oven: Preheat your oven to 350°F (175°C).
• Bake the cookies: Bake the cookies for 10-12 minutes, or until the edges are lightly golden. Keep an eye on them, as baking times can vary depending on your oven.

Step 6: Make the glaze

• Prepare the glaze: While the cookies are baking, whisk together the powdered sugar, milk, and vanilla extract in a small bowl. Add more milk if necessary to reach your desired consistency. The glaze should be smooth and pourable.

Step 7: Drizzle the glaze

• Cool the cookies: Allow the cookies to cool for a few minutes before drizzling the glaze over them.
• Serve and enjoy: Drizzle the glaze generously over the cookies and enjoy the perfect combination of cinnamon sweetness and creamy glaze.