Preheat oven to 325F/160C, grease a 9 x 5 x 3-inch loaf pan and dust with flour, shaking out excess.
Sift flour, baking powder, and salt twice and set aside.
Beat butter until light & creamy. While beating, gradually pour in sugar, then increase speed and beat until light and fluffy.
In a separate bowl, whisk together the eggs to blend but do not add air.
Add beaten eggs in 3 additions, beating for 20 seconds after each addition.
If batter looks like it is starting to curdle, wrap a warm, dish towel around the bowl and continue beating. Add in orange and zest.
Fold in flour by hand in 2 additions and then add the raspberries, spread batter into prepared pan.
Warm the jam in the microwave until fluid (about 30-45 seconds).
Add the jam in individual droplets all over the top of the batter and then use a toothpick or skewer to swirl them.
Bake for 65 to 70 minutes, until a tester inserted in the center of the cake comes out clean. Allow cake to cool for 15 minutes, then turn out onto a rack to cool completely.
While cake is cooling prepare glaze. Heat orange juice, sugar and zest until sugar dissolves. While glaze and cake are still warm, poke holes in cake with a skewer and spoon glaze over cake. The syrup will soak in and set with a crunchy exterior, and the zest will rest on top.
To keep the raspberries from adding too much moisture to the cake, they need to be coated in flour before adding them to the batter.
You can use frozen raspberries for this recipe, but make sure they are fully thawed and drained of excess juices, and then you can coat them with the flour.
To get the swirling effect, warm the jam in the microwave until fluid, and then using a teaspoon, add the jam in individual drops all over the top of the batter and then use a toothpick or skewer to swirl them.