In a food processor, pulse the flour and salt. Add the butter and process briefly. Sprinkle over the ice-cold water and pulse for about 5 seconds, until just moistened.
Transfer the dough to a floured work surface and knead it 2 or 3 times until it comes together. Pat the dough into a disc. Lay a sheet of baking parchment on your work surface and dust it with flour.
Roll out the dough like a pizza to make a 35cm circle, 4–5mm thick. Transfer the parchment to a baking sheet and chill the pastry.
Preheat the oven to 220°C/Fan 200°C/Gas 6. Toss the rhubarb in a bowl with the orange zest, sugar, salt, juice and wine and mix well. Arrange the rhubarb on top of the pastry and sprinkle over any remaining sugary mixture.
Leave a border of 5–6cm around the edge of the pastry, fold that in and crimp to form a border. Brush the fruit with melted butter and sprinkle with caster sugar, then repeat this process three times.
Bake the galette for 10–12 minutes, then lower the oven temperature to 200°C/Fan 180°C/Gas 5 and bake for a further 30–35 minutes.
To make the glaze, cook the rhubarb trimmings with 75ml of water until soft. Strain the liquid from the pulp and add the 2 tablespoons of sugar.
Pour this back into the pan and let the sugar dissolve, then reduce to a thick syrup. Leave the galette to cool, then brush it with the glaze. Serve with vanilla ice cream or whipped cream.