Remove the stems and seeds from the sweet peppers, Italian red peppers, and poblano. For a milder jam, remove the seeds and membranes from the jalapeños.
Finely dice all of the peppers and onion so they cook down evenly.
Heat a medium saucepan over medium heat with a small drizzle of olive oil.
Add the onion, sweet pepper, Italian red pepper, poblano, and jalapeño.
Cook for 6–8 minutes, stirring occasionally, until the vegetables begin to soften.
Add the garlic and cook for another minute.
Add the apple cider vinegar, honey, maple syrup, lemon juice, salt, smoked paprika, black pepper, and red pepper flakes if using.
Stir well and bring the mixture to a gentle simmer.
Reduce the heat to medium-low and simmer uncovered for 20–25 minutes, stirring occasionally.
The vegetables should become very tender and the liquid should reduce into a glossy syrup.
If you want a smoother jam, use the back of your spoon to mash some of the peppers as they cook.
In a small bowl, whisk together the cornstarch and water to make a slurry. Stir it into the pepper mixture and cook for another 1–2 minutes, stirring constantly, until the jam thickens.
Remove from the heat and taste. Add another small splash of vinegar if you want more tang, a little honey or maple if you want it sweeter, or another pinch of red pepper flakes for more heat.
Let the jam cool for about 10–15 minutes. It will continue to thicken as it cools. Transfer to a clean airtight jar or container and refrigerate.
