Put the sugar and measured cold water into a frying pan and heat gently, stirring very occasionally until the sugar has completely dissolved. Bring to the boil and cook for 3–4 minutes, without stirring, until the syrup is just changing colour and is golden around the edges.
Add the measured boiling water, standing well back as the syrup will spit, then tilt the pan to mix. Add the blueberries and cook for 1 minute. Take the pan off the heat and set aside to cool slightly (maybe while you eat your main course).
Mix the fromage frais and custard together, spoon into small dishes, then spoon the blueberry mixture over the top. Serve immediately, with baby meringues if liked.