Preheat oven to 350°F (180°C). Line a 9-inch square baking pan with parchment paper, letting excess extend over sides of pan.

For the crust: In a large bowl, stir together flour, sugar, orange zest, and salt. Using your hands, cut butter into flour mixture until mixture is crumbly. Press into bottom of prepared pan.

Bake until golden and puffy, 15 to 18 minutes. Let cool completely.

For the cranberry curd: In a medium saucepan, combine cranberries and sugar. Cook over medium heat, stirring frequently, until mixture comes to a boil and cranberries begin to burst, 10 to 15 minutes.

In the work bowl of a food processor, process egg yolks until combined. With food processor running, carefully pour hot cranberry mixture through food chute, processing until smooth. Return mixture to saucepan.

In a small bowl, stir together cornstarch and 2 tablespoons (30 grams) water. Pour cornstarch slurry and cinnamon into cranberry mixture, and stir until well combined. Cook over medium heat, stirring constantly, until mixture thickens and cornstarch flavor is cooked out, about 5 minutes. Stir in butter, and remove from heat. Pour cranberry mixture on top of prepared crust, and smooth with an offset spatula. Cover with plastic wrap, pressing wrap directly onto surface of curd to prevent a film from forming. Let cool at room temperature for 1 hour; refrigerate until fully set, at least 4 hours. Slice into 18 (3x1½-inch) rectangles.

For the meringue: In the bowl of a stand mixer, place lemon juice. Using a paper towel, wipe down sides and bottom of bowl with lemon juice until nothing remains. (This will help remove any oils and excess moisture from the bowl.) Let dry.

In the top of a double boiler, whisk together egg whites and sugar. Cook over simmering water, stirring occasionally, until sugar fully dissolves and an instant-read thermometer registers 150°F (66°C), 5 to 7 minutes. (Sugar is dissolved when you can rub the mixture between your fingers and feel no sugar.)

In the cleaned bowl of a stand mixer fitted with the whisk attachment, carefully place egg mixture. Beat on low speed until bubbly. Add cream of tartar, and beat on medium speed until glossy, stiff peaks form, 5 to 7 minutes. Spoon meringue into a pastry bag fitted with your favorite piping tip, and pipe on top of cranberry bars. Using kitchen torch, carefully brown meringue.