Preheat the oven to 170C/325F/gas 3.
Prepare a rectangular 20 x 30cm flan or cake tin: line it with parchment and grease it lightly, or butter and flour the bottom of the tin.
Sift the flour with the baking powder into a large bowl.
Add all the other sponge ingredients.
Beat with a handheld mixer or in a standing mixer with the paddle attachment for a couple of minutes, until the batter becomes creamy and smooth.
Spoon it into the prepared tin and bake for 20-25 minutes until the sponge springs back when lightly pressed.
Loosen the sides with a palette knife; turn the cake out onto a wooden board smooth side down, then carefully peel off the parchment.
Turn the cake right side up onto a wire rack and cool completely.
In the meantime lightly whip the cream.
Using a heart shaped biscuit cutter cut out hearts from the cooled sponge.
Spread some jam over half the hearts (on the side that was bottoms of the cake) and spoon the whipped cream on the other hearts.
Sandwich them together and dust with icing sugar before serving.
