Take the gallon of milk (3,8 L) and pour it into a large pot, minus ¼ cup (59 ml), we need to save that for later. Make sure you have a lid a available for the pot you’re using.Bring the pot almost to a boil, and then turn of the heat.Let it cool until the temperature reaches 105-118 degrees (40-48 degrees Celsius). Meanwhile continue with the next step.Mix together ¼ cup (59 ml) of plain Greek yogurt and the ¼ cup (59 ml) milk that we reserved in step 1.When your big pot has reached 105-118 degrees (40-48 degrees Celsius), remove the film on the top. Then throw in the yogurt/milk we mixture we made in step 3.Whisk everything up nice and gently, then cover the pot with a lid.Wrap the pot in a towel and leave it in your oven overnight with the oven light on (between 9 and 16 hours). This will keep the milk incubated at 100-110 degrees (38-43 degrees Celcius).After the time is up your yogurt is ready!Now it’s time to make this yogurt Greek! Use a cheesecloth or tea towel and start draining it inside a colander. You should let the yogurt strain at room temperature.Squeeze the towel every few hours to make it drain faster.After about 6 hours your Greek yogurt is ready!Put the yogurt in an air tight container and refrigerate until you want to eat it!Don’t throw away the whey that’s left from the straining process, it can be useful for other recipes.