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1
Put 1 3/4 cups lukewarm water (105 degrees F to 110 degrees F), the yeast, 1/2 cup olive oil and 1 tablespoon each turbinado sugar and salt in the bowl of a stand mixer fitted with the dough hook attachment.
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2
Mix on medium speed until the yeast and sugar dissolve, then let stand until foamy, about 10 minutes.
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3
Add both flours and mix on medium speed to make a smooth but sticky dough, about 4 minutes.
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4
Poke the butter pieces into the dough, spacing them evenly apart.
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5
(Do not mix.)
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6
Cover the dough with plastic wrap and set aside in a warm place until doubled in size, 45 minutes to 1 hour.
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7
Mix the dough with the dough hook on low speed just until there are streaks of butter throughout, about 1 minute.
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8
Put the grapes and raisins in a microwave-safe bowl, cover loosely and microwave until juicy, about 10 minutes.
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9
Let cool, then strain through a sieve, discarding the liquid.
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10
Brush a rimmed baking sheet with 2 tablespoons olive oil.
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11
Divide the dough in half and transfer one piece to the baking sheet, leaving the other in the bowl.
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12
Cover both pieces of dough loosely with parchment paper; set aside until plump and airy, about 30 minutes.
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13
Meanwhile, put a pizza stone or inverted rimmed baking sheet on the lowest oven rack and preheat the oven to 450 degrees F.
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14
Spread the dough on the baking sheet so it fills the pan, dimpling it with your fingertips.
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15
Scatter half of the grape-raisin mixture evenly on top.
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16
Put the remaining piece of dough on top and stretch and pat it to cover the bottom piece of dough.
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17
(Don't worry if the dough tears.)
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18
Scatter the walnuts and the remaining grape-raisin mixture on top; dimple the dough all over with your fingertips, poking the topping into the dough.
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19
Cover loosely with parchment and set aside until the dough rises above the sides of the baking sheet by about 1/2 inch, 35 to 40 minutes.
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20
Mix the remaining 1/4 cup sugar, the coriander, rosemary, the remaining 3/4 teaspoon salt and the pepper; sprinkle over the dough.
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21
Place the baking sheet on the hot stone and bake 10 minutes.
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22
Reduce the oven temperature to 400 degrees F and bake until the focaccia is golden and springs back when pressed, 20 to 30 more minutes.
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23
Brush with the remaining 2 tablespoons olive oil; let cool in the pan 15 minutes, then transfer to a rack to cool slightly or let cool completely and freeze.
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24
MAKE IT AHEAD Let the focaccia cool completely, then wrap in foil and freeze for up to 1 week.
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25
Reheat, wrapped, at 450 degrees F until warmed through, about 25 minutes.
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26
Photograph by Con Poulos
