Mix the flour, salt, sugar and yeast in a bowl. Add the butter, milk and egg, mix and knead to form a soft, smooth dough. Cover and leave to rise at room temperature for approx. 1 hr. until doubled in size.
Mix all of the ingredients for the filling in a bowl. On a lightly floured surface, roll the dough out into a rectangle (approx. 40 x 50 cm). Spread the filling on top, leaving approx. 1 cm free around the edges. Roll the dough up from the long edge, without exerting pressure, cut it into approx. 10 pieces using a bread knife. Spread the swirls out evenly in the prepared tin, cover and leave to rise at room temperature for approx. 30 mins.
Approx. 45 mins. in the lower half of an oven preheated to 180°C. Remove the cake, allow to cool in the tin for approx. 10 mins., remove the tin frame, slide the cake onto a cooling rack, leave to cool. Dust with icing sugar.