Preheat oven to 350°F (175°C). Line an 8x8 or 9x9-inch square baking pan with parchment paper, leaving an overhang on two sides.

Make the crust: In a bowl, whisk flour, sugar, and salt. Cut in cold butter and vanilla until mixture resembles damp sand. Press firmly into the prepared pan. Bake for 18-22 mins until edges are light golden. Let cool slightly.

Make the curd: In a saucepan, combine cranberries, sugar, water, orange juice, and zest. Cook over medium heat for 8-10 mins until cranberries pop. Puree until smooth, then strain through a fine-mesh sieve into a bowl.

In a separate bowl, whisk egg yolks and whole egg. Slowly whisk in about ½ cup of the warm cranberry puree to temper. Pour the egg mixture back into the saucepan with the remaining puree.

Cook over low heat, stirring constantly, until thickened (about 5-7 mins). Remove from heat. Stir in salt. Whisk in room temperature butter, one piece at a time, until smooth and glossy.

Pour the warm curd over the warm crust. If using streusel, combine all streusel ingredients in a bowl, cutting in butter until crumbly. Sprinkle over curd.

Bake for 10-15 mins (or 5-7 mins without streusel) until curd is set. Let cool completely on a wire rack, then refrigerate for at least 4 hours, preferably overnight.

Use parchment to lift bars from pan. Place on a cutting board, dust with powdered sugar, cut into squares, and serve.