Heat the milk to 32°C and add the culture and mould according to your particular brand instructions. Add the yoghurt and stir well.
Maintain 32°c and leave to stand for 1 hour
Add the rennet according to the instructions for your brand.
Leave to stand for 30 minutes until a "clean break" is achieved i.e. when the curds break away when pressed with the back of a finger leaving straw coloured whey to fill the gap. It may take longer than 30 minutes.
Gently cut the curds into 1" cubes and then stir gently for 5 minutes before letting them rest for 15 minutes. During the rest give a brief gentle stir every 3-5 minutes to prevent the curds from matting together.
At the end of the rest remove about 3-4 pints of whey with a jug gently pressed into the surface of the curds and whey. Repeat the 15 minute resting and stirring. The curds will shrink during this time releasing more whey. Maintain the temperature at 32°C.
Transfer the curds to a large mould lined with cheese cloth and allow them to drain for several minutes. Pulling up the cloth will aid the drainage.
Now pack the curds gently into the final mould without any cheese cloth. I only have one large mould and so I transfer the curds to a small bucket between draining and packing. The curds around the bottom and sides of the mould can be pressed into place but those in the centre should be left loose as they fall; this ensures that there are air pockets in the centre of the cheese to allow the blue mould to grow.
Once packed into the mould maintain the temperature at 32°C in the mould for another 4 hours. I do this by placing the mould back inside the double boiler but standing on the small bucket lifting the mould out of the water. Place a board on the mould and turn it 5 minutes after filling and then frequently during the 4 hour period.
Leave overnight at room temperature in the mould. The next morning the cheese should be consolidated enough to remove it from the mould and salt it. This cheese is dry salted on the outside. This means adding the salt at about 2-2.5% of the cheese's weight to the outside surfaces over a period of 4 days. For my 4 gallon cheese, the finished cheese weighed 2.4Kg and I added 50g (2.1%) of salt divided into 4 doses.
Mature the cheese at 11 - 12°C and 93-95% RH for about 90 days. After a couple of weeks poke holes in the cheese with a skewer about a couple of inches apart.
I like to wipe the surface occasionally to keep the mould under control. I do this with a piece of cheese cloth moistened in salty water. Be careful not to close up the holes.
Eat.