Melt 2 Tbsp butter in a large skillet over medium heat. Once melted, add corn kernels to skillet and let sit for about 4 minutes before stirring. Let sit for another4 minutes and stir again. Repeat a couple more times until the corn is nicely browned. Remove corn to separate bowl and keep skillet to use in step 3.
While corn is browning, bring a large pot of salted water to a boil and add fettuccine to it. Cook until al dente. Before draining, reserve ¾ cup of water. Put pasta back into the pot.
Put remaining 2 Tbsp butter in skillet over medium heat and when melted, add garlic to the pan. Cook for about 2 minutes, until garlic is softened. Stir the flour into the garlic and then whisk in the milk, cream, salt, and leftover water from the pasta until you have a smooth sauce. Once smooth, whisk in the Greek yogurt and chipotle peppers.
Pour the sauce over the pasta in the pot. Add in corn, avocado, feta, and basil and toss until well combined.