Mix together the dried yeast, sugar and warmed buttermilk and allow to sit for 15 minutes. Stir in the eggs and vanilla. Place the flour and salt into a mixer fitted with a dough hook and add in the yeast mixture. Mix together to start to bind and mix for 3 minutes. Add in a few cubes of margarine, before adding in all the remaining margarine and knead together for 8 minutes until smooth. Place into a lightly greased bowl, cover and leave in the fridge overnight. When ready, cut into 3 balls and roll out thinly. Mix together the melted butter, brown sugar and cinnamon for the filling. Spread ½ of the filling  on top and cover with another layer of dough. Spread over the remaining filling and cover with the last piece of dough. Press together tightly and press a glass into the middle. Cut into 16 pieces, leaving them attached to the middle circle. Twist two ends together outwards, then wet and press the ends together. Repeat with the remaining 14 pieces. Allow to proof for 35-45 minutes then bake in the oven at 200°C for 30-35 minutes (you may need to cover with foil half way. Finish off with glace icing and serve whilst still warm.