Pre heat the oven to 200oC, 180oC fan, gas mark 6.
Line a 32cm x 24cm Swiss roll tray with baking parchment.
Place the margarine, Total Sweet and vanilla into a mixing bowl.
Beat for 4-5 minutes in a machine, occasionally scrape down the sides and beater to ensure a nice even mix.
Once creamy, add 2 tbsp. flour (as Total Sweet is granular, you need to add flour to ensure the egg binds) and beat well.
Next add the eggs and beat until creamy, then add the flour and beat together for 15 seconds or so, do not overbeat.
Spread evenly into the lined Swiss roll tray.
Bake for 15 minutes until risen and springy.
Meanwhile, break the blueberries and the 15g Total Sweet with a fork so you have a rough puree.
Once the sponge is cooked, remove and cool, then turn out the sponge and peel away the parchment, cut in half, across the shortest side.
Spread over the blueberry puree and top with the second piece of sponge, press down lightly.
Cut into 2cm pieces and place half into a deep bowl or small bowls.
To make the custard place the powder into a bowl and add 3-4 tbsp. of milk and mix well. Boil the rest of the milk and as its just boiling whisk in the powder and milk. The custard will thicken straight away.
Remove from the heat add the 60g Total Sweet and vanilla and mix well.
Pour half the custard over the sponge in the bowl, then add the rest of the sponge, finally add the rest of the custard, then cool and chill well.
Lightly whip the fromage frais and add the 10g Total Sweet and vanilla.
Spoon over the chilled custard, then top with grated low sugar dark chocolate, more defrosted blueberries and serve.