Begin by heating 1 cup of sugar in a 3-quart pan over medium heat. Let it melt and turn amber, stirring now and then, for 8-10 minutes. Then, add 3/4 cup of boiling water and stir until it thickens, about 5 minutes. Let the syrup cool down completely.
In a big bowl, mix 1 cup of sugar, 2 and 1/2 cups of cake flour, 4 egg whites, 1/2 cup of sour cream, 1/2 cup of oil, and a bit of salt. Stir until it's thick and a bit sticky. Then, add the cooled syrup slowly, mixing well each time. This makes the cake moist and full of flavor.
Preheat your oven to 350°F (177°C). Grease a 9-inch cake pan with butter or spray. Put parchment paper in it for easy removal. Pour the batter in and smooth the top. Bake for 24 minutes, or until a toothpick comes out clean. Let it cool before frosting and serving.