Roasted Asparagus Soup with Lovage and Dill

When we moved to this house 31 years ago, the backyard was a flatland save for two sticks that called themselves trees, a three foot lilac bush and a small 4 x 10 empty garden plot.  My Dad, an avid gardener, came over armed with cuttings from his herb garden - thyme, sage, chives, garlic chives, oregano and lovage.  he told me that the lovage would give me years of wonderful celery flavor for soups and stews and would grow like a bush every year.  Well, 31 years later, the two sticks are over 50 feet tall, the lilac is huge and the lovage comes back every year.

1 Tbl olive oil
3/4 pound green asparagus, trimmed
3/4 pound white asparagus, trimmed
3 Tbl butter
1/2 cup thinly sliced shallot
1 1/2 cups peeled and diced new potatoes
6 cups chicken broth
3 Tbl chopped lovage ( or celery leaves if you can't get lovage)
1/2 cup chopped fresh dill
1 Tbl dried dill weed
salt and white pepper to taste
sour cream for garnish (optional)

Rub the asparagus with the olive oil and roast in a 400F oven for 20 minutes. Let cool a bit and then cut into 2 inch pieces.
Sweat the shallots in the 3 Tbl butter until soft.
Stir in the potatoes and lovage and add the broth.  
Bring to a boil and simmer until the potatoes are tender, about 8 minutes.
Remove from the heat and stir in the fresh and dried dill and the asparagus.
Process in a food processor or blender in batches, until smooth.
Reheat and season to taste with the salt and white pepper.  Garnish each serving with a dollop of sour cream if desired.
NOTE: This soup is also good served cold.