Heat the oven to 220C / 425F and line a sheet pan (33 x 46 cm / 13 x 18 inch) with parchment.

Pat the potato cubes dry with a kitchen towel, then toss with olive oil, smoked paprika, salt, and black pepper in a large mixing bowl.

Spread the potatoes in a single layer on the sheet pan, leaving space between the cubes so they roast instead of steam.

Roast for 35 to 40 minutes, flipping once at the halfway point, until the edges are deep golden and crisp and the centers are fork-tender.

While the potatoes roast, heat olive oil in a 20 cm / 8-inch saucepan over medium heat. Add the onion and cook for 5 minutes until soft.

Stir in the garlic, smoked paprika, and red pepper flakes. Cook for 30 seconds until fragrant.

Add the tomato paste and cook for 1 minute, then stir in the crushed tomatoes, sherry vinegar, sugar, and salt.

Simmer for 12 to 15 minutes, stirring occasionally, until the sauce thickens enough to coat the back of a spoon. Blend with an immersion blender for a smooth texture, or leave it chunky.

Whisk the mayonnaise, grated garlic, lemon juice, and a pinch of salt together in a small bowl to make the aioli.

Spoon the roasted potatoes onto a platter, cover with the bravas sauce, and drizzle with aioli. Scatter parsley and flaky salt on top and serve right away.