Prep the peaches: Blanch peaches in boiling water for 30 seconds, then transfer to ice water so the skins slip off easily. Pit and slice the peaches into chunks.

Combine in the crockpot: Add the sliced peaches, brown sugar, granulated sugar, lemon juice, cinnamon, nutmeg, vanilla, and salt to the crockpot. Stir until the peaches are evenly coated.

Cook covered: Cover and cook on low for 4 hours. The peaches should be soft and releasing plenty of juice.

Blend until smooth: Use an immersion blender to puree the mixture directly in the crockpot, or transfer to a blender in batches. Blend until smooth, or leave some texture if you prefer a chunkier butter.

Prop the lid open: Place a wooden spoon under the edge of the lid so steam can escape. This step is essential for reducing the liquid and thickening the butter.

Continue cooking: Cook on low for another 5 to 6 hours, stirring every hour, until the mixture darkens to a deep amber and thickens noticeably.

Run the spoon test: Spoon a small amount onto a cold plate and let it sit for a minute. If it holds its shape without liquid pooling around it, the butter is ready.

Cool slightly: Turn off the crockpot and let the peach butter cool for about 15 minutes before jarring or storing.

Jar for the fridge: Ladle into clean jars and refrigerate once cooled to room temperature, where it keeps for up to 3 weeks.

Can for long-term storage: For shelf-stable jars, ladle hot peach butter into sterilized jars leaving 1/4 inch headspace, then process in a water bath canner for 10 minutes.