4 cups all-purpose flour plus additional for dusting
4 teaspoons baking powder
2 teaspoons baking soda
1 1/2 teaspoons salt
1 1/2 teaspoons ground ginger
1 3/4 cups sugar
2 oz crystallized ginger, coarsely chopped
3/4 cup well-shaken buttermilk
1/2 stick (1/4 cup) unsalted butter, melted and cooled slightly
2 large eggs
12 cups vegetable oil
2 cups Lime Leaf-Key Lime Curd
A 1 3/4-inch round cookie cutter
Whisk together flour, baking powder, baking soda, salt, and 3/4 teaspoon ground ginger in a large bowl. Whisk together 1 cup sugar and remaining 3/4 teaspoon ground ginger in a shallow bowl. Pulse remaining 3/4 cup sugar with crystallized ginger in a food processor until ginger is finely chopped. Transfer to a bowl and whisk in buttermilk, butter, and eggs until smooth. Add buttermilk mixture to flour mixture and stir until a dough forms (dough will be sticky). Turn out dough onto a well-floured surface and knead gently just until it comes together, 10 to 12 times, then form into a ball. Lightly dust work surface and dough with flour, then roll out dough into a 13-inch round (about 1/3 inch thick) with a floured rolling pin. Cut out rounds with floured cutter and transfer to a lighly floured baking sheet. Gather scraps and reroll, then cut out additional rounds. (Reroll only once.) Heat oil in a wide 5-quart heavy pot until thermometer registers 375 degrees. Working in batches of 7 or 8, carefully add rounds, one at a time, to oil and fry, turning over once, until golden brown, 1 1/2 to 2 minutes total per batch. (Return oil to 375 degrees between batches.) Transfer to paper towels to drain. Cool slightly, then dredge in ginger sugar. Gently slice donuts in half and spoon Lime Leaf-Key Lime Curd on bottom half of donut; top with second half of donut. Serve 3 or so to a plate, garnish with slices of crystallized ginger.
Doughnuts can be fried (but not dredged in ginger sugar) 4 hours ahead and cooled completely, then kept in an airtight container at room temperature. Reheat undredged doughnuts on a baking sheet in a preheated 250 degrees oven 10 to 15 minutes, then cool slightly and dredge in ginger sugar.
Recipe adapted from Gourmet Magazine