Place your oven rack in center of your oven. Preheat oven to 425℉ / 220 ℃. Line with aluminum foil or parchment paper for easy cleanup.
Wash 2 red peppers and arrange them whole on the baking sheet.
Once the oven has preheated, put the baking sheet and peppers in, and cook for 20 minutes,
Use tongs to turn peppers over. Cook for another 10-15 minutes. You'll know they're finished when the skin has blistered and started to pull away from the rest of the pepper. It's fine if some of the skin has blackened, but don't burn them.
After removing the peppers from the oven, allow them to cool enough that you can touch them without burning your fingers. They don't have to come all the way to room temperature.
Using your fingers, peel the skin away from the peppers, and discard the skin.
Slice the peppers into long strips and place them into a Mason jar.
Peel the 6 cloves garlic and add to the jar along with the peppers. Sprinkle with 1 teaspoon Kosher salt and ½ teaspoon black pepper, and drizzle 3 tablespoons olive oil over the top.
Top with 2 cups white vinegar or as much as needed to cover the peppers. Close the lid, and marinate in your refrigerator for 1 hour or longer.