With a paring knife, slice a shallow "x" into the bottom of each peach. Fill a large bowl with cold water and ice.
Bring a large pot of water to a boil. Drop a few peaches into the boiling water for 30 seconds. Use a slotted spoon to remove the peaches from the water and immediately place them in the ice water. Repeat with the remaining peaches.
Fill another large bowl with water and add the lemon juice.
Starting with the corners of the "x" on the bottom of the peaches, use your fingers to peel the skin off. Place the peeled peaches in the lemon water to prevent them from browning.
Slice the peaches and discard the pits. If desired, scrape the red flesh from the cavities (as it browns over time). Return the peaches to the lemon water while you prepare the syrup.
In a large saucepan, combine the quart of water and 2 cups of sugar over medium heat and stir to dissolve the sugar. Add the vanilla bean, if using. Add the sliced peaches and bring to a boil, then turn off the heat.
Place the sliced peaches in sterilized jars, packing them fairly tightly. Pour the hot syrup over the peaches into the jars, leaving 1/2 inch head space. Discard vanilla bean. Wipe the tops of the jars clean and cover with lids.
Process jars in a large pot of boiling water for 20 minutes, making sure the jars are completely covered with water the entire time.
Let cool completely. Then store in a cool dry place and consume within a year.