Random Recipe: Cream of Arugula Soup

I've been eating a lot of arugula the past 6 months, mostly in salads. A friend recently made a cream of arugula soup that was delicious but I wanted to try my own. I looked at a million recipes and came up with this. A word of warning: white pepper is really distinctive; if you don't like it, leave it out or use just the tiniest amount to start. You could also veganize this recipe by definitely adding potatoes, using veggie broth, eliminating the cream and parmesan and replacing these with, say, two tablespoons of miso. Would be delicious. Just watch the other salt you add since miso is so salty.

2 T butter
2 T olive oil
1 red onion
2 leeks
5 cloves garlic
2 bunches arugula
4 C. chicken or veggie broth
lots of coarse black pepper, at least a 1/2 tsp, but probably more
about 1/4 to 1/2 tsp salt, probably more, to your taste
1/4 tsp crushed red pepper flakes, more crushed
8 oz whipping cream, 1/2 and 1/2 or milk, as you see fit.
1 cup shredded/shaved parmesan (a coarse microplane zester is the best preparation for this)
1/8 tsp ground white pepper
1/8 tsp fresh nutmeg
1/4 tsp dry mustard
1/8 tsp lemon zest

Wash the arugula. If using bunches, cut off some of the stem; if using bagged baby arugula, leave it as is.  
Heat the oil and butter together in a dutch oven or soup pot.  Chop the onion and slice the leeks (white and a little bit of the green part only).  Add the onion and leeks to the butter/oil and saute over medium heat until soft.  Mince and add the garlic and saute a little longer.  Add the arugula and cook it a bit and to wilt it, stirring frequently.  Add the crushed red pepper, some salt, and the black pepper.  
Add the 4 cups of broth.  Bring the mixture to a simmer and let the arugula cook a little longer.  Blend the soup, either with an immersion blender or in batches in a regular blender.  
Return the soup to low heat and add the cream, parmesan, white pepper, dry mustard, and nutmeg.  Stir well to blend.  Taste the soup.  Adjust seasonings to your taste.  There should be some heat behind it provided by the mustard, white pepper, black pepper, and crushed red pepper so if you don't want it to have a pungent, deep, but overall mellow spiciness, adjust.  Just before you serve it, add the lemon zest.