5 Meyer lemons, washed
Place a few small plates in the freezer.
Halve the Meyer lemons lengthwise, then slice into 1/8" thick segments (try to remove all of the seeds and tougher membranes as you do this.)
Measure the sliced lemons in a measuring cup. You should have about 4 cups of sliced fruit at this point, but the more important part is that you use equal amounts of fruit, water, and sugar by volume, so just adjust the amount based on how much fruit you have. Use equal parts demerara sugar and white sugar.
In a medium pot, bring the sliced fruit and water to a boil. Once boiling, reduce the heat to a simmer and cook until fruit is very tender (a good judge is if you can cut through the skin with a wooden spoon.) Add the sugar and return to a boil, then reduce to a simmer for 30 minutes.
After 30 minutes, take a plate out of the freezer and dollop a small spoonful of marmalade onto the plate. Tilt the plate to check the viscosity. It should be thick and jammy and not runny. Continue to simmer the mixture if it is too thin.
Cool before serving or storing. Marmalade will last about a month in the fridge.