French Blueberry Flan Tart

Pastry Crust
7 Make a batch of pate sucrée at least 2 hours before you want to assemble the tart. Divide the dough in two halves, shape into discs, cover in plastic wrap and refrigerate for a minimum of 1 hour. (I usually make mine the day before.)
Line the Tart Ring
10 I am using a French style tart ring that is 22cm x 3.5cm. But you can use a 9-inch (22cm) fluted tart pan that is 1.5 inches (3.5 cm) deep. 
4 Roll out one half of the pastry dough to 1/8–1/4 inch (3–4 mm) thick. Place the tart ring on top and cut out a circle for the tart base. Remove the excess dough and chill the pastry circle in the refrigerator until firm. 
3 Take the second half of the dough and roll it out to the same thickness as the base. Using a ruler, cut strips slightly wider than the height of your tart ring. For a 22cm × 3cm tart ring, I cut the strips 4cm wide. Transfer the strips to the refrigerator to chill until firm before using them to line the tart ring.
5 Line the inside of the tart ring with the chilled strips, sealing any overlaps with your fingertips. Press the dough firmly into the corners and against the sides of the ring to ensure a snug fit and straight, even edges.
6 Place the tart base on a perforated silicone mat set on a baking tray. Position the lined tart ring over the base and press down firmly to seal. Dock the base with a fork, then trim any excess dough with a small knife. Freeze the tart shell until completely firm before par-baking. (1-2 hrs or even better overnight)
Par-bake the Crust
8 Preheat a conventional oven to 375°F (190°C), or if using convection fan oven 350°F (170°C).
9 Bake the empty tart shell for 18-20 minutes until lightly golden in color. Set the pan on a cooling rack and let the crust cool completely. Do not remove the tart ring or tart pan.
11 ~If the dough is properly lined, there's no need for parchment paper or baking weights. However, if you're new to using a tart ring or prefer extra insurance, line the frozen tart shell with parchment paper and fill it with pie weights, dried beans, or rice. Bake 15 min. with weights and 3-5 min. without.
Flan pastry cream filling
13 Set up your work station so everything is laid out and next to the stove to make things easier and less stressful for you. Place an empty bowl on the counter close by. 
14 Stir together the milk, cream, half of the sugar, and vanilla in a large saucepan on medium heat. 
15 ~Option to bring the mixture to simmer, cover with plastic wrap and let steep for an hour for a more intense vanilla flavor. But you can skip this and the flan will still taste amazing. 
16 Meanwhile in a large mixing bowl hand whisk together the eggs, yolks, and remaining half of the sugar into a thick liquid. Use a little elbow grease and whisk in the sifted cornstarch until completely dissolved into a smooth mixture.
17 Once the milk and cream reach a simmer, slowly pour half into the eggs while continuously whisking to temper the mixture.
18 Now pour the egg mixture back into the saucepan while stirring on medium heat.
19 Continuously whisk as the custard starts to thicken. This will happen pretty quickly in just a minute or two. It's important to keep whisking to prevent a lumpy custard. 
20 As it thickens it will come to a boil.  You'll notice it's ready when you stop whisking and the mixture kind of burps up a few air pockets. Whisk vigorously for a smooth glossy pastry cream and then remove from the heat.
21 Transfer the pastry cream to a heat proof bowl, place a sheet of plastic film directly on the surface and refrigerate until cool. 
Assemble & Bake
27 Toss the blueberries with a little lemon juice and sugar in a small bowl until well coated. Set aside.
23 Preheat a conventional oven to 375°F (190°C), or if using convection fan oven 350°F (170°C).
24 Whisk the cold pastry cream a few times by hand to smooth it out.
25 Fill the partially baked tart shell with the pastry cream, but leave a little room for it to puff in the oven. You may have a little cream left over. 
26 Level with an offset spatula. Cover the pastry cream with the sugar coated blueberries. Leave a bare border about 1/2 inch wide of pastry cream next to the crust. Gently pat the berries into the cream. 
28 Bake the flan tart on the middle oven rack for 40-50 minutes. The filling will puff up near the crust and begin to brown slightly. The berries will shrivel and  leak their juice across the top. If you wiggle the flan it should have a slight wobble to the center, similar to cheesecake or pumpkin pie. 
29 Place the pan on a wire to cool completely (3-4 hrs.). The flan will set more firmly as it cools. Leave it in the tart ring or pan.
30 Transfer the cooled flan to the fridge to set overnight or a minimum of 6 hrs. When it has completely set, you can remove the tart ring or tart pan before serving.
31 If the tart crust is slightly attached to the ring or tart pan, you can run a small sharp knife around the edge to loosen it.