This all-purpose vegetable stock has woodsy undertones from the mushrooms and subtle sweetness from the parsnip.
Combine all ingredients in a Dutch oven; bring to a boil. Reduce heat, and simmer until reduced to 6 cups (about 1 hour). Strain stock through a sieve into a large bowl; discard solids. Refrigerate leftover stock in an airtight container for up to 1 week or freeze for up to 3 months.