I added 8L of water to the stockpot and heated to 69 degrees C. Then added the bag and 2500g of Marris Otter Pale Malt. And topped up with hot and cold water, stirring with each addition, until the stock-pot was nearly full and the temperature was 66 degrees C. I then wrapped in a dressing gown and a sleeping bag and waited for 90 minutes. I was amazed that the wrapping managed to keep the heat in for the mash, I barely lost any at all - less than a degree. After removing the bag, letting it drip, and squeezing, I got 9L of wort at (I think) 1.064.
I brought the stockpot bag to the boil and boiled with the schedule:
19g Challenger for 90 minutes
7g Goldings for 10 minutes
1/2 tsp Irish Moss for 10 minutes
1/2 tsp yeast nutrient for 10 minutes
4g Goldings at flame out.
I was amazed at the amount of break material in the pan at the end of the boil. I cooled in the sink, replacing the water a couple of times. I'd cleaned and sanitised the bag during the boil and used it as a sieve to remove the break material whilst pouring into the sanitised fermenter. I think I got 5L after the break material was out and measured it at 1097! I may have made a mistake somewhere along the line.
Because it measured so high I started diluting with water, I slightly misjudged the amount to use and ended up with 13L at 1.042. The target was 1.047. I could have made it up with extract, but I wanted this first one to be a purely grain batch. Good-old Nottingham yeast went into the fermenter.