• Begin by preparing the pan that you will be baking the cake in; I used a 1/4 sheet baking pan (that's 9.5" x 13"). Line the pan with parchment paper and lightly brush the pan's edges with a little oil. (I usually prefer to lightly oil cake pans and dust them with flour rather than using parchment paper. However, because of the large surface area in this case, I wanted to make sure I could flip the cake out of the sheet pan without any part of it sticking.) Set aside, turn your oven on to 350°F and start working on the cake.
• In a medium mixing bowl, combine the flour, cardamom, baking powder, ground almonds or walnuts and salt, and mix thoroughly with a spatula to make sure that everything is well blended. The purist in me is reluctant to mix different nuts, but you can be playful here and substitute other nuts and mix and match and discover new great options. Set aside for now.
• Separate the eggs into two large mixing bowls. Make sure that there's plenty of room in each bowl, as more ingredients will be added to the yolks, and the whites will get whipped up.
• Whisk the egg whites until they form soft peaks. Whisking egg whites by hand is a lost art, but actually can be done with a little patience. Otherwise, use your electric mixer to speed up the process and get to eating the cake faster! Fluffy egg whites add a tremendous amount of lightness and air to this cake. Set aside while you work on the yolks.
• Add the saffron rose water, sugar, yogurt and oil to the bowl with the egg yolks and mix. You can use an electric mixer or a whisk. Mix until well blended and creamy-looking in texture. Add the flour and nut mixture to the egg yolks and mix with a whisk or a spatula until all the lumps disappear. Resist overworking the batter.
• Now comes the fun part: folding the egg whites into the cake batter. I use a spatula for this task and am very methodical to make sure that I don't let out the air that I worked so hard to build into the egg whites. I scrape the spatula around the bowl and under the batter, and then flip it around and bring it back to the top. This way the eggs whites get blended in without too much stirring.
• Pour the cake batter evenly over the sheet pan , jiggle it around gently to make sure it is spread to all the edges. Make sure you don't knock the air out!
• Bake for about 30 minutes. The cake will have risen slightly, but not too much since the batter was spread out. The top should be nicely golden and the edges slightly browned and pulled away from the sheet pan. Test with a toothpick to make sure it is fully cooked in the middle.

Sharbat (syrup)

• While the cake is baking, combine the lemon zest, lemon juice, honey and rose water in a small saucepan, and gently heat until everything is well mixed. No need to cook this for long and as a matter of fact make sure it is not boiled so to preserve the freshness of lemon zest and the scent of rosewater.

Assembly and presentation

• When you take the cake out of the oven, keep it in its pan and place the pan on a cooling rack. Immediately pour the syrup evenly over the entire surface of the cake and allow to sit for 15 to 20 minutes. By then the cake will have absorbed all the syrup, and will be very moist.
• This next step is just a little tricky in that you will need to flip the cake over twice! But if you have been practicing flipping Persian rice out of the pot to display the Tahdig, this should come to you naturally. Swiftly and confidently are the magic words here!
• I use two cutting boards to do this. First, flip the cake onto a cutting board and remove the parchment paper. Then, flip the cake onto a second cutting board so that the top of the cake is back on top again. This will make it look much better for presentation.
• Once you are done with all the flipping, cut the cake into 1 inch long diamond shapes with a sharp knife. You might need to rinse and wipe the knife edge a few times to make sure it continues to cut cleanly without getting the cake too crumbly.
  
• Garnish each piece with ground almonds or pistachios and rose petals, and place on a serving platter.
• Leftovers should be kept in an airtight container and placed in the freezer.