Combine egg yolks, sugar, salt and dry mustard in mixer bowl; mix for 1 minute on low speed with balloon whip. Scrape down sides with spatula; make sure all dry ingredients are dissolved.
With mixer on high speed, alternate slowly, drizzling oil and vinegar into mixture. Alternate oil and vinegar 4 times throughout mixing.
With mixer still running, add lemon juice. Cover, label, date and refrigerate.Makes 1 gallon Source: