Wash the peaches and apples thoroughly. Leave the skins on both fruits. Cut the peach in half, remove the pit, and slice it thinly. Core the apple and slice it thinly.
Add 1 cup water and 1 cup packed light brown sugar to a medium saucepan over medium heat. Stir until the sugar dissolves completely.
Add 4-5 white peach slices, 4-5 apple slices, 1-2 cinnamon sticks, 2 sprigs of rosemary, and 4 whole cloves.
Bring the mixture to a gentle simmer, then reduce the heat to low.
Cover with a tight-fitting lid and simmer for 20-25 minutes.
Remove from the heat and allow the mixture to steep for an additional 10 minutes.
Strain the syrup through a fine-mesh strainer, gently pressing the fruit to release the juices.
Allow the syrup to cool completely before using.
Transfer to an airtight container or jar and store in the fridge.