Sausage Rolls

Name: Sausage Rolls
Prep time: 20 min
Cook time: 1 h 10 min
Total time: 1 h 30 min
Cuisine: European, British
Ingredients: 220 g plain flour, plus extra for rolling; 170 g unsalted butter, diced (1 cm), then frozen; 1 pinch fine sea salt; 80 g water, cold; 150 g onions, quartered; 450 g good quality pork sausagemeat; 1 tsp dried mixed herbs; 1 pinch ground black pepper; 1 egg, beaten, for glazing