Combine chopped peaches, sugar, and lemon juice in a medium saucepan over medium-high heat.

Bring the mixture to a boil, stirring constantly, and boil for 1 minute.

Reduce heat to medium and cook for about 10 minutes, stirring often, until the liquid reduces by about one-third.

Lower the heat to a gentle simmer and continue cooking until the jam reduces by about half and thickens noticeably.

Test for doneness by dragging a spatula across the bottom of the pan; the bottom should remain visible briefly before filling in.

Remove from heat and cool for about 30 minutes.

Transfer to a clean airtight jar or container.

Refrigerate for 30 to 60 minutes before serving to allow the jam to thicken further.