Mix the flour and salt in a bowl. Add the butter and rub together using your hands to form an even, crumbly mixture. Pour in the water and vinegar, then mix quickly to create a soft dough – do not knead. Cover and chill for approx. 30 mins.
Heat the oil in a pan, sauté the Brussels sprouts for approx. 3 mins. Drizzle with the honey, season and leave to cool.
Set aside 2 tbsp of parmesan, mix the rest of the parmesan and the bacon in with the Brussels sprouts.
To shape and fill the galettes
On a sheet of baking paper, roll the pastry into a circle approx. 3 mm thick. Spread the Brussels sprouts on top, leaving approx. 4 cm free around the edges. Brush the edges with egg, fold halfway in, press down gently, brush the edges with egg once more. Top with the reserved parmesan.
Approx. 25 mins. in the centre of an oven preheated to 180°C.