Genoise sponge

Method

1. Start. Warm eggs and sugar over barely simmering water to 105°F / 40°C.Watch for: Use gentle heat and stir often; remove from the heat as soon as the mixture is uniform so residual heat does not take it too far. Apply a thin, even coat and keep it off cut edges or seams unless the step says otherwise.
2. Then. Whip to thick ribbon stage; fold in sifted flour, then tempered butter.Watch for: Use a clean bowl and check the stated stage by lifting the whisk; stop as soon as the foam holds that shape. Cut through the center and sweep up the side while rotating the bowl; stop when the last dry streak disappears so you preserve air and tenderness.
3. Finish. Bake in an 8-inch lined pan 24–28 minutes.Watch for: Begin checking at the early end of the range; use the stated color, movement, or internal-temperature cue rather than time alone.