For the pastry, place flour, sugar and 1 tsp salt flakes in a bowl. Add butter and toss to coat. Using your fingertips, roughly rub butter into dry ingredients, leaving plenty of big pieces of butter. Combine vinegar and 1/4 cup (80ml) iced water in a jug. Add to flour mixture, stirring to combine. Turn out onto a clean work surface and gently knead until the dough comes together. Press to a rough rectangle shape. Enclose in plastic wrap and chill for 2 hours.
Place white chocolate, butter, almond meal and caster sugar in a bowl and, using your fingertips, rub together to combine. Add 1 egg, flour and 1 tsp vanilla, and stir to form a thick paste.
On a lightly floured work surface, roll out pastry to a 3mm-thick large rectangle, trimming to form a clean edge. Place on a lined baking tray. Spread the white chocolate mixture over the pastry, leaving a 7cm border, then fold the pastry edges in to enclose the filling. Lightly beat the remaining egg and brush the edges with eggwash. Scatter with demerara sugar. Chill for 20 minutes.
Preheat oven to 200°C. Place tart in oven and bake for 30 minutes until pastry is golden and cooked through. Cool to room temperature
Combine creme fraiche, lemon zest and remaining 1 tsp vanilla in a bowl and spread over frangipane. Toss strawberries, icing sugar and lemon juice in a bowl.
Scatter dressed strawberries over creme fraiche and serve immediately.