Preheat the oven to 170°C fan, gas mark 5. Line a 21cm square
cake tin with baking parchment. Put the pecans on a baking tray
and bake for 10 minutes, until golden and fragrant. Meanwhile,
put the white chocolate on a separate lined baking tray and bake
for 10 minutes until deeply caramelised. Set both the pecans and
chocolate aside.

Combine the butter and both sugars in a medium saucepan over
a low heat to melt, stirring occasionally. Take off the heat and
allow to cool slightly.

Beat the eggs, then beat into the butter and sugar mixture along
with the vanilla. Beat in both flours and salt. Very roughly chop
the pecans, then stir through the mixture, together with the
white chocolate. Put into the prepared tin, sprinkle with coarse
sea salt, if desired, and bake for 22-25 minutes, until risen and
golden on top. Allow to cool completely in the tin before slicing
into 16 squares.