Wash your rose petals to get rid of dirt and bugs by swirling them in a large bowl filled with cool water. Remove from water and let air dry, about 15 minutes.

Put the rose petals in a bowl with 1 cup of the sugar and massage together with your hands, covering the petals in sugar and massaging them until they’re fragrant and lightly wilted. This helps infuse the sugar with the aroma of the petals. Set aside. 

Add the remaining sugar to a large pot and cover with 1 ½ cups water. Heat the mixture over medium heat, stirring occasionally. Let the sugar dissolve, 5-6 minutes, then add in the rose mixture, along with another ½ cup water. Bring to a boil, then stir once and then lower to a simmer. Skim any foam off with a spoon.

Let the mixture simmer for around 45-50 minutes, until the petals become tender, stirring occasionally to prevent burning. Once the petals are tender, strain the mixture, removing the petals from the liquid and setting aside. 

Return the liquid to the pot and add the cornstarch, whisking to create a slurry. Continue reducing the liquid over medium-low heat for around 15 minutes until gooey. In the last five minutes, add the lemon juice and the vanilla extract. Stir to combine. Reincorporate the petals into the jam.

Once the consistency of the mixture is jammy (the petal pieces should still have a little bit of light texture to them) take it off the stove and let it cool. Sterilize jars and fill. Let cool, then store in a dark pantry. Refrigerate once opened.