Pre-heat oven to 150°C (fan forced) and finely chop walnuts and pecans. In a large bowl, mix together nuts, sugar and cinnamon and set aside.
Unroll the filo pastry, trim to fit a tin 20x20cm and cover with a damp cloth. Brush the bottom of a 20x20cm square tin with melted butter and place a sheet of filo pastry into the tin. Brush melted butter onto the sheet of filo and top with another sheet. Butter and repeat until you've used 5 sheets of filo pastry.
Divide the nut mixture into 3 equal portions (85g per portion) and sprinkle one third over the pastry layers in the tin. Repeat the pastry and buttering process with 5 more sheets of filo and top with another third of the nuts. Repeat with butter and pastry sheets again, top with nuts, then one last time with 5 more sheets of pastry and butter.
Using a sharp knife, cut halfway through the layers (lengthwise into 4 and crosswise into 4) to end up with 16 pieces in total. Bake in 150°C fan-forced oven for about 1 1/2 hours or until top is golden brown. Remove from oven.
In a microwave safe container, heat honey until hot, then gently pour over hot baklava as soon as it comes out of the oven. Allow to cool in the tin on a cooling rack. Keep at room temperature, covered with aluminum foil.
To serve, cut all the way through the layers to remove the pieces from the tin.