Preheat oven to 180 degrees C (350 F).

In a large bowl, mix together egg yolks, flour, baking powder, oil, pandan juice, and 1/2 cup of sugar.

Whisk until smooth.

In another large bowl, beat egg whites, salt, and cream of tartar until stiff peaks form.

Gradually add in 1/3 cup of sugar and continue to beat until very stiff peaks form (approximately 3-4 minutes on high speed).

Gently fold the flour mixture into the egg whites in 2 batches, taking care to keep as much air bubbles in the mixture as possible.

Pour mixture into an ungreased 10.5" tube pan.

Bake in preheated oven at 180 degrees C (350 F) for 25 to 30 minutes.

Allow the cake to cool in the pan for 10 minutes, then invert onto cooling racks to cool completely.

For the Frosting: Sift cocoa powder, sugar, and all-purpose flour.

In a saucepan, heat sifted cocoa powder, sugar, sifted flour, pandan juice, and egg over low heat while gently whisking continuously.

Gradually add in the butter and continue whisking while heating until the desired consistency is reached.

Frost the cake only after it is completely cooled.