Preheat oven to 350°F (177°C). Grease a 9x13-inch baking dish with butter.
Bring a large pot of salted water to a boil over high heat, and add the San Giorgio macaroni. Cook according to package directions, or until al dente (tender but still slightly firm). Drain and set aside.
In a medium saucepan over medium-low heat, melt the butter. Add the flour and stir to combine, cooking for about 2 minutes. Slowly add the milk, stirring constantly to avoid lumps. Increase heat to medium-high and bring the mixture to a gentle boil, stirring occasionally.
Reduce heat to low and simmer for 5 minutes or until thickened. Add salt and pepper, then stir in the cheddar cheese. Stir until melted and combined.
Combine cooked macaroni with cheese sauce in the baking dish. Bake for 25 minutes, or until the top is golden brown and bubbly.
Let cool slightly before serving.