Start by making the pastry, if making your own. Add the butter to the flour and rub with your fingertips until the texture resembles breadcrumbs (alternatively, this can be done in a food processor). At this stage, add in the water until a dough forms. Wrap and chill in the fridge for 15 minutes.
Preheat the oven to 200C/180C Fan/Gas 6. Lightly grease a 23cm loose bottomed tart tin with oil/butter.
Roll the pastry to about 1-2 cm thick, enough to cover the tin. Press to the edges and cut off any excess around the edges. Bake Blind: Place a circle of greaseproof paper on top of the pastry - enough to go up the sides. Add in baking beans/uncooked rice so that the base is entirely covered and weighed down. Bake for 10 minutes, before removing the paper/beans/rice, then bake for a further 5-10 minutes, until the pastry is just cooked and lightly golden.
Once the pastry has cooled a little (at least 15 minutes), spread over the lemon curd.
Make the frangipane by first mixing the butter and sugar on high with an electric mixer for 3-5 minutes - until light and fluffy.
Add in the eggs and almond extract. Then gently fold in the ground almonds and lemon zest. At this stage coat the blueberries in a little flour (to stop them sinking), and gently fold into the batter.
Pour this batter over the lemon curd covered pastry base. Sprinkle over some flaked almonds and bake the entire thing for 35-40 minutes, until golden on top. Let cool on a wire rack.
If using, make the glaze once the tart has cooled by combining the icing sugar and milk and drizzling over. Slice and serve.