Turn oven on to Broil. Place peppers on a baking sheet. Allow to roast for 20 minutes, turning half way through broiling, until peppers are soft & the skin is blistered and dark.
Remove from oven and place in a plastic bag for 8-10 minutes to cool. Remove from bag and you should be able peel the skins off easily. Dice the peppers and set aside until ready to use.
In a large heavy bottomed pot over medium-high heat, melt butter. Add flour and cook for 1 minute, stirring constantly. Add leeks and garlic, cooking for 2 minutes.
Add the already cooked poblano peppers, corn, potato, chicken stock, milk and half & half. Bring to a boil, then lower heat to medium-low and simmer for about 30 minutes, uncovered, until potatoes are cooked through.
Remove from heat and stir in sour cream, salt and pepper. Taste soup and adjust additional seasonings as needed to fit your tastes. Garnish soup with cilantro and serve immediately!
