I've used PC stoneware for years (I used to be a consultant - till I got all the pieces

) but I've also used their new very heavy metal pan - and that works great too! The trick is to have the correct size pan and for it to be nice and sturdy - anything which twists and "pings" as it heats/cools is a no no!
I've tried various recipes (including the PC one) and this was recently voted best by DS(11)'s Scout troop (and leaders!)
175g/6oz walnuts or pecans, chopped roughly
115g/4oz plain chocolate (or a mix of plain and milk)
175g/6oz butter
1t vanilla essence (which I left out as I hate it!)
3 eggs
115g/4oz plain (all purpose) flour
1 level t baking powder
1.Grease baking tin and line with parchment. Break chocolate into pieces and melt in a bowl over a pan of simmering water with the butter, stirring gently until they melt together (do not let the water touch the bottom of the bowl).
2. Pour melted butter and chocolate into alarge bowl and stir in sugar and vanilla.
3. Whisk eggs in another bowl and beat into the chocolate mix a little at a time using a wooden spoon.
4. Sift in flour and baking powder and add nuts. Stir together until well mixed.
5. Pour mixture into tin and smooth top, bake for approx 40 mins at 180C/350F/gas 4.
6. Let mixture cool slightly, then cut into squares and transfer to wire rack to cool further (important - sample a few while warm to make sure they are OK

)
7. Hide from kids and DH in an airtight tin and they will last a few days.
ETA I made them without nuts for scout camp in case of allergies and they turned out just fine.