Preheat the oven to 350 °F (180 °C) and grease two round 8-inch (20 cm) tins.
Sift the flour, baking powder and salt into a large bowl.
Add the sugar and mix to combine.
In another bowl, beat the eggs, orange juice, milk, oil and orange zest.
Add half the orange mixture to the dry ingredients and beat only until incorporated. Scrape down the sides of the bowl with a spatula so nothing is left unmixed.
Add the rest of the orange mixture and beat again just until combined. Stop as soon as the streaks disappear: beating further develops the gluten and makes the cake dense.
Divide the batter between the two tins and bake for about 35 minutes, until a skewer in the centre comes out clean.
Let the cakes cool in their tins on a rack for about 15 minutes.
Turn them out of the tins and let them cool completely. Assembling them warm melts the jam and makes the layers slide.
To assemble: place the first layer flat side up on a plate and spread the jam over it with a spatula, in a thin, even layer. Set the second layer on top and dust with powdered sugar.
Cut with a slightly damp knife, which stops the sponge dragging, and serve.