Cook potatoes in boiling water for 6-8 minutes.

Peel and dice potatoes into 0.5 inch chunks.

Heat butter in a heavy 4-quart saucepan.

Add potatoes, celery, parsnips, carrots to the saucepan.

Cook, uncovered, stirring occasionally, until lightly browned.

Sprinkle with flour and stir until well coated.

Add chicken stock, marjoram, salt, pepper, and mushrooms.

Bring to a boil, stirring constantly.

Reduce heat to very low and partially cover the pot.

Simmer for 25 minutes, or until potatoes are tender.

Taste and adjust seasoning as needed.