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1
Make the streusel In a stand mixer fitted with the paddle, beat all of the ingredients together at medium speed until crumbs form.
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2
Transfer the crumbs to a bowl and press into clumps.
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3
Refrigerate until chilled, about 15 minutes.
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4
Meanwhile, prepare the fruit Set up a gas grill for indirect grilling, then heat to 300.
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5
In a medium bowl, toss the peaches with the blueberries, sugar, lemon juice and cornstarch.
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6
In a 12-inch cast-iron skillet, melt the butter over low heat.
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7
Remove from the heat.
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8
Scrape the fruit and any juices into the skillet.
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9
Make the cake In a medium bowl, whisk both flours with the graham cracker crumbs, baking powder and salt.
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10
In a stand mixer fitted with the paddle, beat the butter with both sugars and the honey at medium speed until fluffy.
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11
Beat in the eggs one at a time, then beat in the buttermilk, oil and vanilla.
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12
Scrape down the side of the bowl and beat in the dry ingredients until just smooth.
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13
Spread the batter in the skillet in an even layer.
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14
Scatter the streusel evenly on top.
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15
Set the skillet on the grill over indirect heat.
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16
Close the grill and bake for about 1 hour and 30 minutes, rotating the skillet every 20 minutes, until a toothpick inserted in the cake comes out clean; keep an eye on the heat to maintain the grill temperature.
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17
Let the cake cool for 1 hour.
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18
Cut into wedges and serve with vanilla ice cream.
