Slice the oranges really thin, approximately 1/8 inch thick. I use a mandolin. Remove the seeds as you go.

Place the slices in a medium saucepan over medium heat.

Add the water, sugar and vanilla. If you are using a vanilla bean, cut it down the middle and remove the seeds and add just the seeds to the pot.

Bring the mixture up to a boil, then turn the heat to low.

Continue to simmer, stirring frequently, until the oranges have darkened in color and thickened to a jammy consistency.

The process can take anywhere from 30 minutes to an hour.

After about 40 minutes check the temperature with a candy thermometer, it should read 222-223 F.

Carefully transfer the marmalade to canning jars and seal with the lid and boil to process the jars.