In a spacious mixing bowl, combine 1 cup of softened unsalted butter and 1 cup of granulated sugar. Beat together on medium speed for about 4 minutes until light and fluffy.

Add 1 large egg and 2 teaspoons of vanilla extract to the creamed mixture. Mix on medium speed until thorough and smooth, about 1-2 minutes.

Gradually add in 2 cups of all-purpose flour, 1 teaspoon of baking soda, and ½ teaspoon of salt. Mix on low speed until just incorporated.

Cover the bowl with plastic wrap and refrigerate for 10-15 minutes.

While the dough chills, mix together ½ cup of granulated sugar and 2 teaspoons of ground cinnamon.

Remove dough from the fridge and scoop out portions, rolling into 16-24 balls. Roll each ball in the cinnamon-sugar mixture.

Preheat oven to 350°F (175°C) and line a baking sheet with parchment paper. Place coated dough balls on the sheet, spaced about 2 inches apart. Bake for 9-11 minutes.

Dust cookies lightly with leftover cinnamon-sugar mixture as soon as you pull them from the oven.

Prepare the filling by melting 1 tablespoon of butter and mixing with 1 can of dulce de leche until smooth.

Spread a layer of the dulce de leche mixture onto the bottom side of one cookie, and place another cookie on top to create a sandwich.

Allow the assembled cookies to rest at room temperature for at least an hour before serving.