Preheat the oven to 350°F (180°C or 160°C for a fan oven).
Grease a 20 cm (8 inch) square cake pan and line the bottom with baking parchment.
For the crumble topping, combine the demerera sugar, flour, rolled oats and cold butter (first 4 ingredients) in a medium bowl.
Cut the ingredients together with a pastry blender or rub with your fingers until the mixture looks like coarse crumbs.
Pour the melted butter into a large bowl.
Stir in the caster sugar thoroughly and then add the lemon juice and zest.
Stir in the buttermilk and almond extract.
Beat in the eggs.
Stir in the flour, baking powder, salt and oats.
Mix until well combined but don't worry if the batter is lumpy, that is because of the oats.
Set the batter aside.
Stir together the cream cheese and lemon curd. Set aside.
Spread a half of the batter in the prepared cake tin.
Spread the lemon curd and cream cheese mixture over the top.
Drop the remaining batter by tablespoons over the top of the lemon curd mixture and spread the batter to cover the top evenly.
Sprinkle with crumble topping.
Bake for 35 to 45 or until a skewer inserted into the centre of the cake comes out clean.
Cool completely before glazing.
To glaze, mix the icing sugar together with enough of the lemon juice to make a smooth, drizzle-able glaze.
Drizzle the glaze over the cake.
Allow the glaze to set before cutting into bars or larger squares.