Cream the Base:
In a large bowl, beat softened butter and sugar until light and fluffy (about 3 minutes).
Add egg and vanilla extract; beat until well combined.

Mix Dry Ingredients:
In a separate bowl, whisk together flour, baking powder, and salt.
Gradually add to wet mixture on low speed until a soft dough forms.

Roll Out Dough:
Divide dough in half. Roll each half between two sheets of parchment paper into a rectangle about 1/4-inch thick.

Prepare Jam Filling:
In a small bowl, mix raspberry jam with cornstarch until smooth.

Spread & Roll:
Spread a thin, even layer of jam on each dough rectangle, leaving a small border.
Starting from the long side, tightly roll dough into a log.

Chill the Dough:
Wrap each log in plastic wrap and refrigerate for at least 2 hours (or freeze for 30 minutes) until firm.

Slice & Bake:
Preheat oven to 350°F (175°C). Slice logs into 1/2-inch thick rounds.
Place 2 inches apart on parchment-lined baking sheets.
Bake for 10–12 minutes, until edges are just barely golden.

Cool:
Allow cookies to cool on the baking sheet completely to firm up.