Preheat oven to 350 degrees. Line a rimmed baking sheet with parchment paper. Place the cherries on the prepared baking sheet, cut-side up. Roast for 30 minutes. Remove from oven and set aside.

Melt butter in a large, heavy-bottomed pot over medium-high heat. Add the onion and sauté until translucent. Add the garlic and cook for another minute.

Add the cherries and remaining ingredients to the pot. Bring to a boil, then reduce heat to low and simmer for 20-30 minutes, stirring occasionally, until slightly thickened.

Remove from heat and blend using an immersion blender until smooth (or allow to cool slightly and blend in a regular blender, but always be very careful when blending hot liquids!). At this point, assess the thickness of your sauce. If you would like it to be a bit thicker, return to the heat and simmer for another 10-20 minutes until your desired thickness. Taste and add more salt or crushed red pepper as needed/desired.

Allow to cool; pour into jars and store in the refrigerator.