Preheat your oven to 350°F (175°C). Grease and flour a 9x5 inch loaf pan.
In a large mixing bowl, cream together the softened butter and sugar until light and fluffy.
Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.
In a separate bowl, whisk together the flour, baking powder, and salt. Gradually add this dry mixture to the wet mixture, alternating with the sour cream, starting and ending with the flour mixture. Mix until just combined.
In a small bowl, gently toss the fresh raspberries with 1 tablespoon of flour to prevent them from sinking in the batter.
Fold the floured raspberries into the batter gently, being careful not to mash them.
Pour half of the batter into the prepared loaf pan. Drop spoonfuls of raspberry jam over the batter, swirl it gently with a knife.
Pour the remaining batter on top and again swirl with raspberry jam, creating a beautiful marbled effect.
Bake in the preheated oven for 55-65 minutes, or until a toothpick inserted into the center comes out clean.
Allow the cake to cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.
Notes
Slice the pound cake and serve on a decorative platter, dusting with powdered sugar and garnishing with fresh raspberries for an appealing finish.