To make the dough, put the flour, salt, sugar and butter in a large bowl and rub together till the mixture resembles breadcrumbs. Add in the zest, yeast and warm milk and mix to a soft dough. Place the dough onto a floured surface and knead well for 4 minutes. Put the dough into a floured bowl, cover with plastic and leave to rise till double in size, for about an hour. Knock back the dough and roll out to a large square, 40cm x 20cm. Brush the dough with half of the melted butter, then evenly spread out the strawberry jam using a palette knife. Sprinkle over the cinnamon and sliced strawberries evenly. Roll up tight from top to bottom, into a large Swiss roll and cut up into 22 equal slices. Brush 2 large muffin baking trays with some of the remaining butter and place a slice of dough into each. Brush with the remaining butter and leave to rise again till double in size again. Bake the buns in the oven at 200`c for 25-30 minutes. Meanwhile, mix the icing sugar with the vanilla and cream cheese to make the frosting. Brush over the cooked buns and decorate with the white chocolate chips and extra strawberries