Preheat the oven to 350°F (180°C / 160°C fan). Lightly grease two 8-inch round cake pans. Line the bottoms with rounds of parchment paper, then lightly grease the parchment if desired.

Place the softened butter and caster or superfine sugar in a large mixing bowl. Using an electric hand mixer, beat them together until the mixture becomes noticeably lighter in color and fluffy.

Beat the eggs together lightly in a separate bowl. Add them to the butter mixture gradually, beating well between additions. If the mixture begins to look curdled, add a spoonful of the measured flour and continue mixing gently.

Sift the self-raising flour and baking powder over the mixture. Using a large spoon or spatula, fold the dry ingredients in gently rather than beating vigorously. Add the vanilla. Fold in about 2 tablespoons of milk, using a little more only if necessary to achieve a soft batter that drops easily from the spoon.

Divide the batter as evenly as possible between the two prepared pans. For the most evenly matched layers, you can weigh the filled pans as you divide the mixture. Gently smooth the tops.

Bake for approximately 20-25 minutes, or until the cakes are golden, have begun to pull very slightly from the sides of the pans, and spring back when gently touched in the center. A toothpick or cake tester inserted into the center should come out clean or with only a few dry crumbs.

Let the cakes cool in their pans for about 5-10 minutes. Carefully turn them onto a wire rack, remove the parchment and allow them to cool completely.

Place one sponge layer on a serving plate with its flattest side facing upward. Spread the jam evenly over the cake, leaving a small margin around the edge. Place the second sponge on top. Don't press down heavily—the weight of the top layer will settle the cake naturally.

Lightly dust the top with caster sugar, superfine sugar or powdered sugar.