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

Add Dry Ingredients: Whisk the flour, baking powder, and salt together. Gradually add to the wet mixture on low speed. Mix just until a soft dough forms.

Roll Out: Divide the dough in half. Roll each half between two sheets of parchment paper into a rectangle (about ¼-inch thick).

Prepare the Jam: In a small bowl, whisk the raspberry jam with the cornstarch. This thickens the jam so it stays inside the spiral.

Spread & Roll: Spread a thin, even layer of the jam mixture over the dough rectangles, leaving a small border at the edges. Starting from the long side, tightly roll the dough into a log.

Chill: Wrap the logs tightly in plastic wrap. Refrigerate for at least 2 hours (or freeze for 30 minutes). This is the most important step—if the dough is too soft, the spiral will smoosh when you slice it.

Slice: Preheat oven to 350°F (175°C). Use a sharp knife to slice the cold log into ½-inch thick rounds.

Bake: Place cookies 2 inches apart on a parchment-lined baking sheet. Bake for 10–12 minutes. The edges should be barely golden. Let cool completely on the baking sheet to firm up.