Peel the potatoes and cut into large chunks. Place in a large pot with cold water, and season with salt. Bring the water to a boil and cook the potatoes until very soft, about 15 minutes.
While the potatoes cook, heat a large skillet over medium heat, add the oil, onion and poblano pepper. Cook until onions are soft and translucent, 5 to 7 minutes. Stir in salt, pepper and cumin and set aside.
Drain potatoes and place them in large bowl. Add the onion and pepper mixture, sour cream, butter, and milk and mash together until smooth. Fold in the onion and pepper mixture.
Add 2 tablespoons of potato mixture to the center of each tortilla and roll into a cylinder. Repeat until all of the ingredients are used. Place the flautas on a baking sheet and cook for 20 minutes. Garnish with cilantro.
For the queso: In a saucepan over medium heat, add butter and oil, then add jalapeños, salt, pepper and diced tomatoes. Stir in milk.
In a small bowl, add grated cheese and toss with flour, then add to pan, stirring to combine and melt.