Preheat oven to 175C/350F. Take an 8 inch (20cm) Square cake tin and line it with baking paper. Make sure the paper is long on 2 of the sides to help remove the cake once the sauce has been added.
Place the egg into the clean bowl of a kitchen stand mixer fitted with a whisk attachment.
Whisk the egg on high for 5 minutes.
Add the maple syrup and vanilla and whisk on high for a further 3 minutes.
Add the milk, lemon zest and lemon juice into the egg mixture and whisk to combine.
In a separate bowl, lightly whisk the coconut flour and baking powder together. Ensure that the coconut flour has no lumps in it.
Turn the whisk to low and add the flour mixture. (If you keep it on high then you will most likely end up wearing the flour). Once incorporated, return the whisk speed to medium/high to fully mix all the ingredients.
Pour the batter into the tin and smooth out the top. Bake for 30-35 minutes or until a toothpick inserted in the centre comes out clean.
Allow the cake to cool in the tin for 30 minutes.
After 30 minutes take the end of a wooden spoon and 'poke' holes in the cake at regular intervals (I did 4 or 5 rows of 5 holes; so 16-20 'pokes'). Do not make the holes too close together and do not push too far down; about 1/2 way is right.
When the cake has cooled pour and spread the lemon curd over the cake, making sure it goes into the poke holes.
Remove the cake from the tin using the longer edges of baking paper and place on a serving tray.
Just before serving make and spread the meringue on top of the cake. Use a blow torch to brown the edges, or place for 1-2 minutes in a hot oven or under a hot grill (keep watch so it doesn't burn). Ther meringue can also be served without browning (it will be like a big gooey marshmallow).
The cake can be served immediately and any left overs kept in the fridge.