Preheat the oven to 350F.

In a small saucepan, melt the butter with the oil over a low heat. Remove from heat and set aside.

Prepare the filling: Place the nuts and sugar in a food processor and pulse until you have a medium-fine mixture. Place the nut mixture into a bowl and add about 4 tablespoons of the melted butter and oil. Mix well and set aside.

Assemble the baklava: Grease a 12 inch baking dish or tin. Fit half the pastry sheets in the dish, one at a time, brushing each generously with the butter and oil mixture. Ease the phyllo pastry into the corners, folding and overlapping as required and trimming the edges if necessary. Be sure to work with one sheet at a time while keeping the rest covered in a clean damp towel, as phyllo pastry dries very quickly. Spread the nut mixture evenly over the sheets. Cover with the remaining sheets of phyllo, one at a time, brushing each, including the top, with the melted butter and oil mixture.

Using a sharp knife, cut about 9 diagonal lines starting from the bottom left corner of the pan, then cut another 9 diagonal lines from the bottom right corner to create diamond shapes. Be sure to cut all the way through to the bottom.

Bake the baklava until the top is golden, about 40-45 minutes

While the baklava bakes, prepare the syrup: In a small saucepan, combine the sugar, water, and lemon juice. Bring to a simmer and cook for 10 minutes, until slightly thickened. Remove from heat, stir in the orange blossom water, and let cool completely in the refrigerator.

Remove the baklava from the oven and let it cool for 5 minutes. Carefully pour the cold syrup evenly over the hot pastry — it should sizzle. For extra crispness, you can return it to the oven for 5 more minutes.

Serve at room temperature. Store in an airtight container at room temperature for up to 5 days.