Place the poblano peppers directly onto a gas burner and turn the flame to high. Using tongs, rotate the poblanos frequently until their skins are blistered on all sides, about 4-6 minutes each. Transfer the bowl and cover with foil or plastic wrap – or even better, if you have paper bags, place them inside and roll the bag up tight. If you don’t have a gas stovetop, this can be achieved under your oven broiler while turning frequently.
In a medium saucepan, heat your stock to a low simmer. On a separate burner, heat a large saucepan or dutch oven over medium heat. Once hot, add oil then add onion and saute until soft and translucent, about 8 minutes. Add the garlic and cook one minute longer. Add the uncooked rice to the pot and stir for a minute or two, until it becomes lightly toasted. Pour in the beer and scrape up any bits that are stuck to the bottom. Let simmer for a minute or so, until the beer has almost disappeared. Ladle one cup of the warm stock into the rice mixture and simmer until absorbed, stirring frequently. Add remaining stock 1/2 cup at a time, allowing it to absorb after each addition. With your last spoonful of stock, add the corn kernels. Once all of the stock and corn have been added to the rice and the stock has been absorbed, stir in the cheese, salt and pepper to taste. Remove from heat.
Preheat the oven to 400°F. Remove the peppers from the bowl or brown bag and gently rub off the skins. Cut each pepper in half and remove the guts as best you can. Fill each pepper with rice mixture and arrange on a baking sheet or in a baking dish. Sprinkle with queso fresco and bake for 10-15 minutes, until they begin to brown.
While the peppers are cooking, stir together the yogurt, lime juice, milk and a pinch of salt.
Remove the peppers from the oven, drizzle with sauce and garnish with cilantro.