Preheat the oven to 325 degrees F. Line 2 baking sheets with parchment paper or silicone baking mats.
Melt the butter in a small, heavy-bottomed saucepan over medium heat. Continue to cook, swirling the pan occasionally, until the butter browns lightly and smells slightly nutty, about 15 minutes. Transfer the butter to a medium bowl -- be sure to get all the tasty brown bits -- and cool slightly.
Meanwhile, whisk the flour, baking powder and salt in another medium bowl.
Whisk the egg yolk, sugar and vanilla into the cooled browned butter.
Stir the dry ingredients into the butter mixture to make a uniform but crumbly dough that looks like wet sand.
Scoop out dough with a small teaspoon (the kind you set the table with, not the ones you measure with). Rock spoon gently back and forth against the side of the bowl, packing the dough into the spoon, then scrape/slide the spoon against the inside of the bowl to make spoon-shaped cookies. Trim excess dough with your fingers and slide out onto the prepared pans, preserving their shape. (Try to make sure you form an even number of cookies, since these sandwich together.)
Bake cookies until just browned, about 12 to 15 minutes. Cool almost completely on the baking sheets, and then transfer cookies to a rack to cool.
When cool, spread 1/2 teaspoon jam on the flat side of a cookie, and then sandwich together with a second cookie. Repeat until all cookies have met their match. Lightly dust the cookies with the confectioners' sugar. Serve.
Busy baker's tips: The dough can be prepared several hours ahead and stored at room temperature. Freeze baked cookie halves wrapped tightly in plastic wrap, followed by aluminum foil for up to 2 weeks. When ready to serve, defrost at room temperature and assemble as desired. Store sandwiches in an airtight container for up to 3 days. Do not store with crisp cookies, as moisture from the jam will soften the texture of other crisp cookies.
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From Food Network Kitchens