Stir the yeast into 250ml warm water and leave for about 5 minutes. Put the flour, 2 tsp salt, milk, brown sugar, lemon zest, cardamom and melted butter into a large mixing bowl, then stir in the yeast water. Mix and knead the mixture for about 8 minutes to make a firm dough that springs back when you press your finger into it, then put it in a large bowl. Leave, covered with a damp tea towel and in a warm place, for approximately 1 1/2 hours or until it is risen and springy. Knock it back by kneading it briefly and divide into 8 or 16 balls.