Over medium heat in a medium-size heavy bottomed saucepan, melt 4 tablespoons of butter.
Whisk in the vinegar. Over low heat whisk in the flour, lemon juice and seasonings. Whisk until the ingredients are fully incorporated.
Beat the egg yolks in a small bowl. To the bowl add 2 tablespoon of the warm liquid whisking constantly to combine and temper.
Slowly drizzle the egg yolks into the vinegar mixture in the saucepan, whisking continually. Cook for 2 minutes.
Remove the saucepan from the stove top and beat in 1 cup of granulated sugar.
Beat for 2 minutes or until the dressing has thickened and is light yellow in color. Pop it into the fridge to cool completely.
After the dressing has cooled pour over the chopped coleslaw and green onions. Mix well. Let the cole slaw chill in the fridge for at least 4 hours. Taste and adjust the salt and pepper to taste. Mix well before serving.