In a saucepan set over medium-low heat, melt the butter until it turns a golden amber color and develops a nutty aroma. Transfer the butter to a heat-safe bowl and allow it to cool until slightly warm.

Preheat the oven to 325°F (165°C). Line two baking sheets with parchment paper and set aside.

In a medium bowl, whisk together the flour, baking soda, and salt. Set aside.

In a separate bowl, beat the cooled butter and granulated sugar until well combined, approximately 1 to 2 minutes.

Add the vanilla extract, whole egg, and egg yolk to the butter mixture and beat until fully incorporated.

Gradually add the dry ingredients to the wet ingredients on low speed, mixing just until no visible flour remains.

To shape the cookies, press a small portion of dough into a teaspoon, leveling the surface and removing any excess dough. Carefully slide the dough out of the spoon using your fingers.

Place the shaped dough onto the prepared baking sheets, flat side down and rounded side facing up, spacing evenly.

Bake for 8 to 10 minutes, or until the cookies are set and lightly colored on the bottom. Remove from the oven and allow the cookies to cool completely on the baking sheets.

Once cooled, spread a thin layer of jam onto the flat side of one cookie and sandwich with another cookie. For best results, refrigerate the filled cookies for 30 to 60 minutes to allow them to set before serving.