Line your 20cm (8 inch) cake tin with parchment paper and preheat your oven to 160 deg C (320F)
Combine the water and sugar in a saucepan on low-medium heat until the sugar dissolves. Add the blood orange slices and bring the sugar syrup to a boil - then simmer for 10 minutes.
Remove the blood orange slices with a slotted spoon and set them aside to cool. Boil the sugar syrup for an extra 5 mins - until it has thickened slightly.
Combine the almond meal, flour, salt and baking powder in a bowl and set aside.
Cream the butter and sugar until it becomes pale and creamy using a stand mixer.
Turn the speed down to low and add the eggs one at a time, ensuring they are well incorporated.
Add the vanilla, zest and add the almond meal mixture in two parts. Stir until just combined.
Line your cake tin with the cooled, cooked blood orange slices.
Spoon the batter into the cake pan, smoothing the top with a knife or spatula and bake for 35-40 minutes until the top has browned and a skewer inserted into the centre comes out clean.
Allow the cake to cool in the cake pan for 10 mins, before turning it onto a cake rack to cool completely. Serve with cream and extra syrup.