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Position racks in upper and lower third of oven. Preheat oven to 325°F (165°C). Line two half-sheet pans with parchment paper; set aside.
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In a stand mixer fitted with the paddle attachment, beat flour, sugar, cornmeal, baking powder and salt to combine. Add butter pieces, beating on medium speed until coarse crumbs form, about 2 minutes. (You can do this with a hand mixer; mixing times will be longer. Use visual cues).
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Reduce speed to low and add eggs, one at a time, beating well after each addition. Keep beating until a stiff dough forms. Beat in macadamias, papaya, pineapple, coconut and ginger. If the dough is too stiff, simply empty dough out of bowl and knead with hands until fruit, nuts and ginger and distributed evenly. Divide dough in half and roll each half into a 12-inch (30.5 cm) log. Transfer logs to one of the prepared pans, separated apart. Pat each log into a 2-inch (5 cm) wide log.
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Bake until golden brown, about 35 to 45 minutes. The logs will be dry to the touch and should feel a bit firm. Leave logs on pan and cool completely on a wire rack. This will take quite a while, possibly up to 30 minutes. Do not rush this step.
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Cut logs crosswise into ½-inch (12 mm) biscotti. I have best success using a chef’s knife and the following technique: Place a log in front of you horizontally, then take the knife and place the tip in contact with the cutting surface on the far side of the log. Use a rocking motion to bring the knife towards you; it will go down into the log, creating the slice. Go slowly and methodically. You will most likely lose a few biscotti to crumbles; don’t fret! Place biscotti evenly spaced apart, cut side down, on both baking sheets.
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Bake, rotating sheets back to front and from one rack to the other halfway through, until just a very light golden color, about 15 to 18 minutes total. Cool cookies completely on pans set on wire racks. Store in an airtight container at room temperature for up to 2 weeks.