Preheat the oven to 180°C/ 160°C fan/ gas mark 4/ 350°F
Line the base of the tin with a liner
Chop the nuts in half
For the White Chocolate Brownies:
Break the chocolate into pieces and put in a bowl with the butter. Melt over a small pan of hot, not boiling, water. Don't let the bowl touch the water.For step-by-step instructions see How to Melt Chocolate
Whisk the eggs with the caster sugar and vanilla extract until thick and pale
When the chocolate and butter have melted, let them cool slightly and stir into the egg and sugar mixtureAlways add warm ingredients to cooler ones for a smooth mixture
Add the nuts and flour and mix in thoroughly but carefully
Pour into the tin and cook for about 20-30 minutes. When they're done the top will be a golden speckle and the inside will still be soft. The edges of the cake will start to come away from the tin.The brownies will continue to cook in the tin when they're out of the oven
Leave in the tin to cool. Cut into squares - they are very rich, so don't be too generous with the size.Keep in the fridge until ready to serve.