Prepare the blueberry jam first. In a medium-sized sauce pot, combine the berries, sugar, orange zest and water. Cook the mixture over medium-high heat, bringing the jam to a simmer. Simmer for about 7 to 8 minutes, cooking the berries until they burst open and the sugar is dissolved. Remove from heat and allow the jam to cool down.
In a small ramekin, combine the 2 tablespoons water with 1 tablespoon unflavored gelatin. Stir to combine the two, then set the gelatin aside to bloom. If preparing this recipe with agar gelatin, add the agar into the custard when heating.
In a large mixing bowl, whisk together the egg yolks, sugar and a pinch of salt. Whisk for 3 to 4 minutes until the yolks are pale in color and mixture ribbons off of the whisk. Pour the milk and cream into a large sauce pot and add the cornstarch. Heat the milk over medium heat, whisking constantly, until the milk is hot but not boiling.
Temper the hot milk into the egg yolks, adding a little bit at a time and whisking vigorously after each addition. Once the two mixtures are combined, pour the resulting custard mix back into the sauce pot. Add the bloomed gelatin, or agar gelatin. Cook the mixture over medium-low heat (avoid high heat, which can cause separation!) and stir constantly with a rubber spatula. The mixture needs to thicken; avoid boiling. Remove the custard from heat and add the vanilla extract and orange zest.
To assemble the dessert, place a few tablespoons of the blueberry jam into the bottom of small ramekins or custard bowls. Ladle the custard over the berry jam, filling the dish to the top. I like to place the dishes onto a small baking tray before filling to easily transfer the dessert into the refrigerator to set. Allow the creme brulee to set in the refrigerator for a few hours, or leave to set overnight.
When ready to serve, sprinkle about a teaspoon over the set custard. Use a kitchen blow-torch to caramelize the sugar. Serve with a few lemon wedges and additional blueberry jam, if desired.