Make the Chiffon Cake:

1. Preheat oven to 350°F (175°C). Line an 8×8-inch pan with parchment paper (bottom only).
2. Separate egg whites and yolks into clean, grease-free bowls.
3. Mix 7 tbsp sugar with orange zest and rub together. Add to yolks and whisk until light.
4. Stir in milk, flour, pistachios, baking powder, and salt. Fold gently.
5. In another bowl, beat egg whites to soft peaks, gradually adding 3.5 tbsp sugar. Continue beating until stiff peaks form.
6. Gently fold the egg whites into the batter in three additions.
7. Pour into the prepared pan and bake for 40-45 minutes. Cake is done when it springs back to touch.
8. Let the cake cool completely before removing from the pan.

Prepare the Milk Mixture:

1. Whisk together evaporated milk, condensed milk, whole milk, and pistachio cream until smooth.
2. Adjust pistachio cream and condensed milk to taste.
3. Add a few drops of green food coloring (optional).

Soak the Cake:

1. Poke holes all over the cooled cake with a fork or skewer.
2. Pour the milk mixture evenly over the cake.
3. Cover and refrigerate for at least 2 hours (preferably overnight).

Make the Whipped Cream:

1. Chill a mixing bowl and beat heavy whipping cream until soft peaks form.
2. Add icing sugar and continue whipping until stiff peaks form.

Frost & Garnish:

1. Spread the whipped cream over the soaked cake.
2. Sprinkle with chopped pistachios and dried rose petals.
3. Slice and serve chilled.