Preheat oven to 160 degrees and line a 22x33cm tin with parchment.

Melt the butter and chocolate in a bowl over a pot of simmering water, being careful not to let the bowl touch the water or the chocolate will curdle.

Then remove from the heat and allow to cool till close to room temperature.

Meanwhile, whisk the beaten eggs until pale and thick – about 7 to 10 minutes. Gradually beat in the sugar. Then fold the chocolate mix into the egg mix.

Sieve the flour in stages into this mixture, folding it in gently as you go.

Finally, fold in the nuts. Turn the whole mixture into the tin and bake for 20-25 minutes. Cool fully before serving. Expect some swooning if you accompany with cream or ice cream.