Melt the butter and add just a tiny bit of oil to it. Pick a suitable container. Pour in 2 tbsp of the fat every 3 sheets.
The walnuts are for 1/2 packet of sheets, so count how many sheets you have ahead of time.
After you've arranged the sheets, cut the baklava into rhombuses. Put it to bake in a preheated 356°F (180 °C) oven.
Prepare a syrup from 2 1/2 cups (600 g) sugar and 1 2/3 cups (400 ml) water. Once it's ready, add the lemon slice to it to prevent it from candying.
It's recommended to pour the hot syrup over the cooled baklava.