Divide the dough into 21 parts, form them into balls and divide up into 3 groups of 7. Roll out the 1st 7 balls into 7 round sheets with a diameter of a dessert plate.
Place the 1st sheet in front of you, sprinkle with starch, place the 2nd sheet on top, sprinkle with starch again and repeat for all 7 sheets. Once you've made a pile of 7 sheets, sprinkle starch on top as well and roll the whole thing out using a rolling pin into 1 large sheet that's the same diameter as the tray in which you'll be baking.
Smear the tray in question with a little oil or butter, place this large sheet in it, sprinkle with walnuts. Repeat this process for the 2nd group of 7 dough balls, sprinkle each with starch and arrange in a pile. Roll it out into 1 large sheet, place it atop the walnut stuffing and sprinkle it with walnuts in turn.
Repeat this process for the final 7 sheets. Put in the tray to cover the other ones underneath. Cut the dough as desired, into rhombuses, pieces or shapes of your choice.
Melt the butter and pour it over the entire baklava, make sure it gets into the cuts as well. Heat the oven to 338°F (170 °C) and put the tray in it, bake until golden - about 50 min. Take it out and leave to cool.
Make the syrup by heating the sugar and water in a pot, add the juice and rind of 1/2 a lemon and bring to a boil. Leave it to boil a bit until it forms a sugar syrup.
Pour the syrup over the cooled baklava. Leave it in the fridge for at least 12 hours to take in the syrup.