Preheat the oven to 350 degrees F (175 degrees C).
Cut off the top of the head of garlic to expose the cloves, trimming about 1/4 inch off of the top of each clove. Brush the cut cloves with a small amount of olive oil and nestle the head into a piece of aluminum foil.
Bake in the preheated oven until cloves are tender and browned, about 45 minutes. Remove from the oven. Increase temperature to 450 degrees F (230 degrees C).
Place 6 to 8 cloves in a blender or food processor. Add butter, salt, and pepper and blend until smooth. Scoop about 2 tablespoons of the mixture into a saucepan over medium heat. Add mushrooms and cook until softened, about 5 minutes. Remove from heat.
Place cherry tomatoes in a bowl, toss with remaining olive oil, and season with salt and pepper. Spread over a baking sheet.
Roast in the oven until soft and browned, about 10 minutes.
Fill a large pot with lightly salted water and bring to a rolling boil. Stir in bucatini and return to a boil. Cook pasta uncovered, stirring occasionally, until tender yet firm to the bite, 9 to 13 minutes. Drain and toss with the mushrooms, roasted tomatoes, and remaining butter-garlic sauce.