In a stock pot over medium heat, cook the bacon until very crispy. Remove from pan and reserve 1 tbsp bacon fat. Set bacon aside.
Melt butter and add bacon fat. Add leeks and cook until soft. Like onions, leeks will cook down quite a bit.
Add flour to make a roux. Let this cook out for a few minutes until it starts to turn a golden blond color.
Add chicken stock and whisk to combine. Add garlic and reserved corn cobs to the pot, and simmer on medium low heat for 20 minutes. Carefully remove cobs from the pot with kitchen tongs and discard.
Add potatoes, simmer for 10 minutes.
Next, add corn, salt, pepper, and thyme. Cook for 3 minutes.
Add bacon and milk, stir to combine, then simmer an additional minute, or until potatoes are fork-tender.
Garnish with fresh parsley, if desired..