• Adjust oven rack to middle position and heat oven to 425 degrees F. Line rimmed baking sheet with parchment paper.

Vanilla Tart Custard:

• In a saucepan pour in the milk and stir in half of the sugar. Over a low heat, warm the milk until the sugar melts, being careful not to scald the milk, about 2-3 minutes. Remove from heat and add vanilla extract, giving it a stir to combine.
• Whisk the egg yolks with the remaining sugar, in a separate bowl until they are pale and fluffy, then add the cornstarch whisking until mixed in. Pour warm milk little by little into the yolk mixture, whisking constantly. When you have mixed in all the milk, pour the mixture back into the pan and place on low heat.
• Slowly warm up the custard, constantly whisking and scraping the bottom of the pan until it thickens enough to really coat the back of a spoon. Avoid over cooking the eggs – keep stirring! Your best tool will be a silicone spatula to ensure no part of the custard stays on the bottom of the pan for too long. The minute it thickens, take off the heat and immediately push through a sieve into a bowl to cool.

Galette Crust:

• You can either make one galette or individual tarts, so cut the sheet of puff pastry as you wish – I opt for using half of one pre-cut sheet and cut it into two sections. Transfer puff pastry to prepared sheet and fold edges of dough over by ¼ inch and crimp to create ¼-inch-thick border.
• Pop it in the preheated oven, for 9 minutes so it begins to puff and you’ll prevent a soggy galette crust bottom.

Galette finishing touches

• Take a few spoons of the custard and spread generously over the inner square of pastry, being careful not to go over the edges. I like to add enough to create a thick layer (about ¼-inch deep or one finger depth) – using almost all of the custard.
• Cut the rhubarb into lengths and place on top of the custard, nestling them into the custard a bit, cramming as much rhubarb on as possible.