Preheat your oven to 350°F (175°C).

In a small bowl, whisk together the flour, powdered sugar, and kosher salt.

In a small saucepan, melt the unsalted butter over low heat, then add the vanilla extract and orange zest. Stir it all together.

Pour the melted butter mixture into the dry ingredients and stir until everything is moistened. Cool slightly to firm up.

Press the dough evenly across the bottom and up the sides of a 9-inch tart pan.

Bake the crust until golden brown, about 20 minutes.

In a medium saucepan, combine cranberries and orange juice. Cook over medium-high heat until cranberries begin to burst.

Pass the cranberry mixture through a fine mesh sieve to separate the solids from the liquid.

Return the strained mixture to the saucepan. Add sugar, eggs, egg yolks, unsalted butter, vanilla extract, and orange liqueur if using. Stir vigorously.

Over medium-low heat, stir constantly until the mixture thickens and reaches 170°F (about 8-9 minutes).

Immediately strain the curd through a fine mesh sieve into a bowl, then pour it into the prepared crust.

Return the tart to the oven and bake until the curd is set, about 10 minutes.

Allow the tart to cool at room temperature for about an hour, then refrigerate to chill.

Combine egg whites and cream of tartar in the bowl of a stand mixer fitted with a whisk attachment.

In a small saucepan, combine the sugar and water. Heat over medium-high until the sugar registers 220°F.

Begin whisking the egg whites on medium speed. Carefully pour in cooked sugar when it reaches 240°F.

Increase the speed to high and continue beating until the mixture forms stiff peaks.

Transfer the meringue to a piping bag and pipe it onto the chilled tart. Optionally, torch the meringue.