In a small bowl, whisk together egg yolks, 2 tbsp of milk, and cornstarch until mixture is all smooth and pale in colour.
Combine milk and whipping cream in a microwave safe container on high power for about 2 minutes. Set aside.
In a medium heavy bottom saucepan, heat sugar and vanilla seeds on medium high heat to make a dry caramel. Try not to stir the sugar, swirl the pan occasionally until the sugar turns into an amber colour. Slowly pour into hot milk/cream mixture, stir the bottom of the pan to ensure the caramel is cooked into the milk. Take out vanilla pod.
Temper egg yolks but slowly adding small amounts of hot milk. Return mixture into pan, heat on medium heat, keep whisking until mixture boils, or when bubbles break the surface. If the pastry cream is lumpy you can strain it before storing it. Transfer pastry cream into a clean container, place a piece of plastic wrap directly on top to prevent a skin from forming. Chill until ready to use.
Almond Cookie Dough + Assembly
In a medium mixing bowl, cream together butter, sugar, and almond flour with a wooden spoon or silicone spatula until light and pale in colour.
Incorporate eggs and vanilla extract, mixing until it is homogenous.
Lastly fold in flour and salt, mixing until a dough forms. Don't overmix. Shape dough into a log, wrap with plastic and chill for at least 2 hours before using.
Preheat oven to 350 F / 175 C.
Take out dough to room temperature to warm up for about 15 minutes before rolling. Knead dough a couple of times to soften. Take half of the dough, dust lightly with flour, and roll into a 10 inch round. Trace and cut out the dough to the size of the bottom of you cake pan. Roll remaining dough into a 1/2 inch diameter rope. Brush the edge of the bottom piece of dough lightly with water. Line the edge with the dough rope and press gently into the bottom.
Fill the center with the pastry cream. You can pipe it in, or just scoop it in with a spoon. Make sure the pastry cream is level before sealing it with the top pastry.
Lightly dust the second half of dough with flour, roll it into a 10 inch round. Trace and cut out a round the size of the top of you cake pan. The size of the top and bottom rounds will be different if you are using a tapered cake pan.
Brush the edges lightly again with water, carefully place the top round onto the cake, and seal by gently pressing the edges with your fingers.
For the finishing touch, brush the whole top with egg wash, using the tines of a fork, lightly score the signature gâteau Basque pattern. Bake in preheated oven for 30-40 minutes, until the top is golden. Cool completely before removing from the pan! Serve at room temperature.