Yes, you can serve mashed potatoes on Yom Tov. Especially when it looks as pretty as this.
Place potatoes in a large pot and cover with water. Bring to a boil over high heat. Boil until tender, about 25 minutes.
Drain and set aside.
Preheat the oven to 400 degrees Fahrenheit.
Place red pepper in a baking pan and drizzle with 1/2 tablespoon olive oil. Place the garlic in a piece of aluminum foil and drizzle with remaining olive oil. Fold up the aluminum foil to enclose the garlic. Place the aluminum packet in the baking pan with the pepper.
Bake until pepper is tender, about 25 to 30 minutes. Let cool and peel the skin off the pepper.
In a large bowl, combine potatoes, pepper, garlic cloves (remove them from the skin), and margarine.
Using an immersion blender, blend until potatoes are smooth. Season with salt and pepper to taste.
If potatoes seem a little runny when blending, add a bit of flour, half a tablespoon at a time.