Preheat oven to 180°C/360°F and adjust a baking rack onto the middle shelf. Grease and line with parchment paper a 8-inch or 9-inch cake pan and set it aside.
In a large bowl, place the egg whites. Using a hand mixer, whisk the whites on medium speed until they become foamy, then increase the speed to high. Continue whisking until the whites turn glossy and stiff peaks form, then set the bowl aside.
In another large bowl whisk the egg yolks and sugar with an hand mixer until light, pale, and fluffy, about 4 minutes. Then gently whisk in the orange zest and juice.
Place a sieve/ strainer over the bowl. Add flour and baking powder, and sift into the cake batter, followed by the almond flour. Whisk until just combined (do not overmix).
Gently fold the beaten egg whites into the cake batter in 3 batches, start at the bottom of the bowl, scoop up the batter, and fold it over the egg whites, until completely incorporated.
Bake in the oven for approximately 40 minutes. During the last 10 minutes of baking time, cover the top of the cake with foil to prevent it from browning too much. To check if the cake is ready, insert a toothpick in the center, if it comes out clean, the cake is ready.
Remove the cake from the oven, allow to cool, then gently remove the cake from the pan.
Once ready, dust the Italian almond cake with powdered sugar and serve at room temperature. It's lovely topped with orange mascarpone frosting, vanilla ice cream, freshly whipped cream, or Greek yogurt.