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1
Heat the oven to 450 degrees F and arrange a rack in the middle.
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2
Place the potatoes in a large pot, cover with water, generously season the water with salt, and bring to a boil over high heat.
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3
Reduce the heat to medium and simmer until the potatoes are knife tender, about 25 to 30 minutes.
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4
Drain the potatoes.
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5
When the potatoes are cool enough to handle, place them on a baking sheet.
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6
Using the palm of your hand, press down on each until flattened to about a 1/2- to 3/4-inch thickness (the skins will split apart and the flesh may crumble slightly).
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7
Whisk together the oil, rosemary, red pepper flakes, measured salt, and pepper to taste in a small bowl until combined.
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8
Using a pastry brush, brush half of the oil mixture over the potatoes and season with salt.
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9
Using a flat spatula, flip the potatoes over, brush the remaining oil mixture over them, and season with salt.
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10
Roast until the bottoms of the potatoes are golden brown, about 20 minutes.
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11
Using the flat spatula, flip the potatoes over and roast until the edges and bottoms are crunchy and golden brown, about 20 minutes more.
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12
Remove from the oven, place the baking sheet on a wire rack, and cover with foil.
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13
Keep the oven at 450 degrees F and arrange a rack in the top position closest to the broiler.
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14
Place the sardines on a baking sheet and season the insides and outsides with salt and pepper.
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15
Combine the olives, parsley, garlic, anchovies, olive oil, lemon zest, lemon juice, measured salt, and pepper to taste in a medium bowl.
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16
Fill each sardine with a few teaspoons of the olive mixture.
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17
(The amount needed will vary depending on the size of your sardines.
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18
Do not overfillthe fish should not be gaping open.)
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19
Scatter any remaining olive mixture around the sardines on the baking sheet, leaving any excess liquid in the bowl.
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20
Sprinkle the breadcrumbs on top of the sardines.
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21
Roast just until the fish are firm and starting to brown at the edges, about 5 to 7 minutes.
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22
To serve, divide the smashed potatoes among four plates.
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23
Lay the sardines over the potatoes and top with any leftover roasted-olive-and-breadcrumb mixture from the baking sheet.
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24
Serve immediately.
