Spread the poppy seed over a baking pan lined with parchment paper and toast for 10 minutes in a 350F preheated oven. Stir on the five minutes mark.
Remove from the oven and set aside to cool.
Set the oven to 320F and line a 9x13-inch pan with parchment paper, making sure not to grease the sides.
In a large bowl, mix the egg yolks, oil, orange juice, orange zest vanilla, and 1 1/4 cup of the sugar (250g) until smooth.
In a separate bowl, mix the flour, baking powder, salt, and poppy seeds.
Gradually mix the flour mixture into the egg yolk mixture. Only stir to incorporate; do not over-mix.
Using an electric mixer or a stand mixer fitted with the whisk attachment, whip the egg whites until frothy. About one minute.
With the mixer on high, gradually add the remaining sugar (1/2 cup, 100g).
Whip until you have a white, shiny, medium meringue. (the meringue will not hold its shape when you dip the whisk and lift it)
Fold the meringue into the orange/yolk mixture, then pour the cake batter into the prepared pan and bake for 35-38 minutes. The cake is ready when a toothpick comes out clean from the center of the cake.
Remove from the oven and allow the cake to cool in the pan. When ready to serve, run a sharp knife against the sides of pan.