Set oven at 375 degrees to preheat. Sift together flour, salt, baking powder 3 times. In large bowl of mixer, beat yolks on No. 10 speed for 2 1/2 minutes. Add hot water gradually while beating, about 1 minute, then continue beating until very thick and light, about 6 1/2 minutes longer. Beat in flavoring, then sugar, sprinkling in a tablespoon at a time, taking 3 minutes. Scrape bowl gently toward beaters with rubber scraper a few times.
Turn to No. 2 speed. Sprinkle in flour mixture evenly and quickly, folding over and over with rubber scraper, about 1 1/2 minutes. Remove from mixer, cut through batter, folding over and over for a few times with rubber spatula. Turn into ungreased pan. Bake about 40 minutes or until done. Invert, leg hang until cold. Remove.
