Preheat oven to 375 degrees.

Cook pasta in a large pot of salted, boiling water until al dente (for elbow macaroni, that's about 7 minutes, for penne, more like 10). Drain and set aside.

Meanwhile, melt butter in a large saucepan over medium heat. Add onion and cook until softened, about 3 minutes. Add garlic and cook 30 seconds. Add flour and cook, stirring constantly, 1 minute. Gradually whisk in milk, a bit at a time.

Bring sauce to a boil over medium-high heat, then reduce to low and cook until thickened slightly, about 5 minutes.

Place the miso paste in a small bowl and slowly whisk in about 1/2 cup of the hot sauce until completely blended. Whisk this miso mixture into the rest of the sauce. Add shredded cheese, whisking until smooth. Whisk in carrot puree, pepper, and salt to taste. Add pasta to the sauce and stir to evenly coat. Transfer pasta to a buttered 2 quart (2 litre) baking dish.

In a medium bowl, combine all topping ingredients and sprinkle evenly over pasta. Transfer dish to oven and bake until topping is golden and sauce is bubbling at edges, about 20 minutes.