Preheat the oven to 180 degrees C. Grease and flour a 1 litre heart shaped cake tin.
Melt the butter with the chocolate in a double boiler or in the microwave. Cool at room temperature.
Separate the egg and with an electric beater whisk the egg white to stiff peaks.
In another bowl whisk the egg yolk with the sugar until fluffy and pale. Then add the melted butter and chocolate then the flour sifted with the baking powder. Gently incorporate the egg white too, with a bottom-up movement of your spatula. Pour the mixture in the prepared tin.
Bake in the preheated oven for 10-15 minutes or until just set. Do not cook too long or the cake will get dry and stiff. Remove from the oven and let cool completely.
With an heart shaped cookie cutter, press the center of the cake and remove it. Mount on a wooden stick and serve as lollipop. Fill the center with chopped strawberries splashed with lemon juice. Serve.