asparagus, celariac and leek soup with tarrgon creme fraiche

Ingredients

• soup
• 1 big fist size celariac peeled and sliced 1/4 in
  
• 3 cups thinly sliced leek (white and pale green only)
  
• 1 pound thick asparagus, bottoms trimmed, cut in 1 in. pieces
  
• 1 clove a garlic sliced
  
• 2 sprigs tarragon
  
• homemade chicken stock to cover veg by an inch
  
• salt and finely ground white pepper
  
• 1 tablespoon butter
  
• 1 tablespoon olive oil
  

• tarragon creme fraiche
• 1 cup creme fraich
  
• 1 tablespoon finely minced trarragon
  
• ¹/₂ teaspoon lemon juice (mayer if possible)
  
• ¹/₄ teaspoon microplaned lemon zest