Sterilize the jars before cooking the jam, set aside.
Clean the peaches under running water, dry them and slice in half. Remove the pit and cut the peaches in small cubes.
In a separate bowl, combine the contents of the Dr. Oetker Gelfix 3:1 package with the 2 teaspoons of extra granulated sugar. Stir to ensure even distribution.
Place the cubed peaches in a large, heavy-bottomed pot. Add the1 & 1/2 cups of granulated sugar to the peaches. Stir to combine. Place the pot over medium heat and bring the peach mixture to a gentle boil, stirring frequently to prevent sticking or burning. Continue cooking for about 20–30 minutes, or until the peaches break down and the mixture thickens.
When the peaches have softened and the mixture has thickened to your desired consistency (usually when it coats the back of a spoon), sprinkle the pectin-sugar mixture evenly over the jam. Stir vigorously to fully incorporate the pectin-sugar mixture. Continue to simmer for an additional 2–3 minutes to ensure the pectin activates and the jam thickens further.
Close the heat and remove the pot from the stove. Immediately fill the sterilized jars with the Peach jam. Fill the jars with a large soup spoon, up to the 1/4 to 1/2 inch of headspace. Be careful with this step, as the Peach jam is very hot.
Once the jars are filled with the Peach jam, wipe the rims with a clean, damp paper towel. Seal the jars with sterilized lids, tighten and turn the jars upside down for 5 minutes.
Let cool the jars for 12 hours. Turn the jars back to the straight position, open and enjoy!