01 - Preheat oven to 375°F. Grease a 12-cup muffin tin or line each cup with paper liners.
02 - Boil salted water and cook elbow macaroni according to package directions until al dente. Drain and set aside.
03 - Melt 2 tablespoons unsalted butter in a saucepan over medium heat. Whisk in 1 tablespoon flour and cook for 1 minute. Gradually add whole milk while whisking until the mixture thickens slightly, about 2 to 3 minutes.
04 - Remove the saucepan from heat. Stir in shredded cheddar cheese, salt, and black pepper until smooth. Fold in cooked macaroni and mix well. Allow to cool slightly.
05 - In a large mixing bowl, whisk together yellow cornmeal, all-purpose flour, granulated sugar, baking powder, and salt.
06 - In a separate bowl, whisk eggs, buttermilk, and melted butter until combined.
07 - Pour the wet ingredients into the dry mixture and stir just until incorporated. Gently fold in drained corn kernels and finely diced jalapeños.
08 - Spoon 1 tablespoon of cornbread batter into the base of each muffin cup. Add a generous tablespoon of the mac and cheese mixture. Top with more cornbread batter to fill each cup about three-quarters full. Garnish with jalapeño slices if desired.
09 - Place muffin tin in the oven and bake for 18 to 22 minutes, until the tops are golden and a toothpick inserted into the cornbread comes out clean.
10 - Let muffins cool in the pan for 5 minutes, then transfer to a wire rack. Serve warm.