Rinse and sort the cranberries, discarding any soft or damaged ones.

In a medium saucepan, combine cranberries, water, and 6 tablespoons sugar. Bring to a boil over medium-high heat, then reduce to medium-low. Simmer for 10–15 minutes, stirring often, until cranberries break down and thicken. Set aside to cool for at least 30 minutes.

Preheat oven to 325°F. Line a 9-inch square baking pan with parchment paper, leaving overhang. Grease well.

In a bowl, mix melted butter, vanilla, 1/4 cup sugar, and salt. Stir in flour until a thick dough forms.

Press dough evenly into the pan, reaching all edges. Bake for 16–18 minutes until lightly golden. Remove, poke with a fork, turn off oven, and cool for 20 minutes.

In another bowl, whisk together 1 cup sugar and 3 tablespoons flour. Add eggs, then lemon juice, whisking until smooth.

Spread cooled cranberry mixture evenly over cooled crust. Refrigerate for 45 minutes.

Preheat oven to 350°F. Pour lemon mixture gently over cranberry layer.

Bake for 43–45 minutes, until the center is set.

Cool at room temperature for 1 hour, then refrigerate 1–2 hours before slicing. Dust with powdered sugar before serving.