To make the meringues, heat the oven to 120C/fan 100C/gas 1/2. Put the egg whites and sugar in a bowl set over a pan of simmering water and whisk until the sugar has dissolved, add the cream of tartar and keep whisking until you have a very thick glossy meringue. Spoon it into a piping bag with a 1cm plain nozzle. Add a stripe of food colouring to the inside of the bag using a skewer, if you want to colour them.
Pipe heart shapes onto baking sheets lined with baking paper and decorate with sprinkles (if using), bake for 1 hour and then cool completely.
Turn the oven up to 180C/fan 160C/gas 4. Beat the sugar, butter and lemon zest using an electric mixer until light and fluffy – give it plenty of time as this will make the cakes nice and light. Add 1 egg at a time with a spoonful of the measured flour to prevent curdling. Finally, mix in the remaining flour and almonds and 2 tbsp lemon juice. Line a bun tin with 12 cake (not muffin) cases and divide the mix between them. Bake for 18-20 minutes, until risen and light golden. Cool on a wire rack.
Beat the butter and icing sugar together to make an icing and add some lemon juice to flavour it. Swirl through some raspberry jam and ice the tops of the cakes – you can pipe the icing on if you like. Put a meringue heart onto each.