Easy 4-ingredient Sponge Cake recipe

0 Start by pre-heating your oven to 350 Fahrenheit, and lining the bottom of a 9-inch cake pan with parchment paper, leaving the sides of the pan ungreased.
1 Over a medium bowl of a stand mixer or electric mixer (you can also use a hand mixer), using the whisk attachment, whip on high speed the eggs and sugar until they triple in size, for around 4-5 minutes.It is key to whip the eggs to just the right volume and no more. If it's whipped too hard and it becomes stiff, it won't rise as it should.Lift the whisk from the batter and make a figure-eight with the dripping batter. If the figure-eight stays on the batter, it’s good to go.
2 Fold in flour into the egg mixture using a spatula, gently mixing it into the wet ingredients until just combined, being careful not to overmix and keeping the batter light and fluffy. This is to avoid popping the air bubbles created by whipping the eggs.
3 Fold in the melted butter, the same way you did with the flour, pour the batter into the pan, and immediately place it in the oven to bake.Bake for 30 to 40 minutes, until a toothpick inserted in the middle comes out clean and your cake looks golden brown.
4 Remove the sponge cake from the oven, place over a wire rack, and let cool for 5 minutes. Then, invert the cake tin into the cooling rack and remove the parchment paper from the bottom of the cake. Leave the cake to completely cool upside down on the wire rack, for around 2-3 hours.