In a food processor, combine all-purpose flour, icing sugar, and a pinch of salt. Blitz until combined, then add cold butter and pulse until breadcrumb texture is achieved. Add lemon zest, lemon juice, and egg; process until dough holds together. Wrap in cling film and refrigerate for at least 2 hours, preferably overnight.

Preheat your oven to 180°C (356°F).

Roll the chilled pastry on a floured surface to about 3mm thick. Transfer to tart tin, pressing into corners and trimming excess pastry. Return to refrigerator to maintain flakiness.

In a baking dish, combine chopped rhubarb, orange zest, and vanilla. Bake for about 10-15 minutes until tender. Set aside to cool.

In a mixing bowl, beat softened butter and icing sugar until pale and fluffy (about 3-5 minutes). Add eggs one at a time, mixing well. Fold in ground almonds until smooth and creamy.

Spread the frangipane filling into the tart shell. Evenly distribute rhubarb and raspberries over the filling, then sprinkle with sliced almonds.

Bake for about 40-45 minutes until frangipane is puffed and golden brown. Prepare almond praline in the last 15 minutes by whisking egg white until soft peaks form and folding in sliced almonds. Sprinkle on top halfway through baking.

Allow the tart to cool on a wire rack for about 15-20 minutes before serving. Enjoy warm or at room temperature.