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1
Preheat the oven to 450F with a rack at the center position.
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2
Line a large, shallow heavy-duty baking pan with aluminum foil.
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3
Place the onions, celery, carrots, fennel, leeks, green pepper, and garlic on the lined baking pan and drizzle with the vegetable oil.
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4
Toss the vegetables to coat them with the oil and roast them in the oven for 30 minutes.
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5
Remove the pan from the oven to stir the vegetables after the first 15 minutes.
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6
While the vegetables are roasting, place the parsley, thyme, bay leaf, peppercorns, and fennel fronds in a piece of cheesecloth and tie securely.
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7
When the vegetables are lightly browned around the edges, scrape them with any accumulated juices into the insert if the slow cooker.
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8
Bury the cheesecloth bag among the vegetables, pour in the water, and add the salt.
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9
Cover and cook on HIGH for 6 hours, until the stock is bubbling, the vegetables are very soft, and the stock is a deep amber color.
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10
Turn the slow cooker off and let the stock cool slightly.
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11
Strain the stock into a bowl.
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12
Press hard on the vegetables and cheesecloth bag, then discard them.
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13
Store the stock in covered containers in the refrigerator for 1 week, or freeze for up to 6 months.
