Preheat oven to 425°F (220°C). Line a baking sheet with parchment paper.
Toss diced potatoes with 3 tablespoons olive oil, salt, and pepper. Spread them evenly on the baking sheet.
Roast for 40 minutes or until golden brown and crispy, flipping halfway through.
Meanwhile, make the bravas sauce: Heat 1 tablespoon olive oil in a saucepan over medium heat. Add onions and garlic, sauté until softened.
Stir in smoked paprika, cayenne, and tomato paste. Cook for 1 minute. Add crushed tomatoes and simmer for 10 minutes. Season with salt and a pinch of sugar.
For the aioli, mix mayonnaise, lemon juice, and grated garlic in a small bowl.
Serve crispy potatoes with a generous drizzle of bravas sauce and aioli on top.