Preheat oven to 350ºF (or 325ºF if convection/gas).
Line an 8×8 metal pan with parchment. Don't use glass, use a metal pan if possible. It bakes more evenly.
Melt butter + white chocolate (microwave or double boiler). Stir until smooth.
Whisk in sugar.
Add eggs one at a time, then yolk + vanilla.
Fold in flour, cardamom, salt.
Stir in pecans.
Spread batter in pan.
Bake ~35 min, until edges are set and toothpick comes out clean. (Tent with foil if browning too fast.)
Cool at least 20 min before slicing.
