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1
Heat the oven to 350 degrees F and arrange 2 racks to divide the oven into thirds.
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2
Line 2 baking sheets with parchment paper; set aside.
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3
Whisk the measured flour, salt, and baking powder in a medium bowl to aerate and remove any lumps; set aside.
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4
Place the butter and sugar in the bowl of a stand mixer fitted with a paddle attachment.
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5
Beat on medium speed until light and fluffy, scraping down the sides of the bowl as needed, about 3 minutes.
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6
Stop the mixer, scrape down the paddle and the sides of the bowl, and add the egg and vanilla.
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7
Beat on medium speed until incorporated, about 1 1/2 minutes.
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8
Stop the mixer and scrape down the bowl.
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9
Add the flour mixture and beat on low speed until the dough just comes together, about 45 seconds.
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10
Turn the dough onto a floured work surface and form it into a disk.
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11
Divide the dough into 4 equal portions.
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12
Using your hands, roll each portion into a 10-by-1-inch log.
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13
Carefully transfer 2 of the logs onto each prepared baking sheet.
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14
Using the handle of a wooden spoon, make a 1/2-inch-wide and 1/2-inch-deep trough in the center of each log, leaving a 1/2-inch border at each end.
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15
Place the jam in a piping bag or a resealable plastic bag (snip off one bottom corner of the plastic bag, if using) and pipe the jam into each of the troughs.
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16
Place both baking sheets in the oven and bake for 10 minutes.
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17
Rotate the baking sheets front to back and top to bottom and bake until the cookie logs are light golden brown around the bottom edges, about 10 to 12 minutes more.
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18
Place the baking sheets on wire racks and let the logs cool for 15 minutes.
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19
Pick up 1 of the parchment sheets and carefully transfer the two logs to a cutting board.
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20
Cut each log on the diagonal into 1-inch-wide pieces.
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21
Transfer the cookies to the wire rack.
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22
Repeat with the remaining parchment sheet and cookie logs.
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23
Let the cookies cool completely.
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24
Store in an airtight container for up to 5 days.
