Preheat oven to 325°F with rack on middle position. Line a baking sheet with parchment paper.
In the bowl of a stand mixer fitted with paddle attachment on high speed, beat butter and sugar until creamy and light, 2-3 minutes. This is where the magic happens, make sure to take the time to beat the butter and sugar until it's nice and fluffy.
Add vanilla and salt, scraping down bowl as needed. Switch to low and slowly mix in flour, just until combined. Dough should be somewhat sticky.
Using a large cookie scoop, scoop dough on to a parchment-lined baking sheets. Take a 1/2 teaspoon dip it in a bowl of flour and press down the center of each ball, making a deep well in the middle.
Fill cookie centers generously with Mixed Berry Jam. I use the the same 1/2 teaspoon that use to make the wells in the cookie to add the jam
Bake 20 minutes or until golden brown and puffy. Let cool 5 min. on baking sheet, then gently transfer to finish cooling on wire rack.
When cookies are completely cooled, dust with confectioners' sugar. Cookies can be kept in airtight container at room temp for a few days.
This cookie dough is less sweet than others, making space for the very sweet mixed berry jam and the generous dusting of powdered sugar at the end.
These cookies are not intended too brown much, as they're more of a shortbread color so keep and eye on them.
Recipe by Whipperberry at https://whipperberry.com/mixed-berry-jam-and-butter-cookies/