Key Lime Coconut Bars

• 1 cup shredded sweetened coconut
• 1 1/2 cups all-purpose flour
• 1/2 cup confectioners' sugar, plus more for dusting tops
• 6 large egg yolks
• 10 tablespoons unsalted butter, cut in small pieces
• 2 cans (14 ounces) sweetened condensed milk
• 4 teaspoons grated key lime or regular lime zest, plus more for garnish (optional)
• 1 cup key lime or regular lime juice

1. Preheat the oven to 350 degrees. Spread coconut on a rimmed baking sheet, and toast until golden brown, 6 to 8 minutes, tossing every 2 minutes to ensure even browning. Remove from oven; transfer to a plate to cool.
2. In a large mixing bowl, combine flour and sugar, and add half the toasted coconut. Using two knives or a pastry cutter, cut the butter into the flour-coconut mixture until it resembles coarse meal. Pat mixture into a 9-by-13-inch pan, and bake until golden, 20 to 25 minutes. Allow to cool slightly.
3. Meanwhile, beat together egg yolks and condensed milk with a whisk until thick. Gradually beat in lime zest and juice. Pour into cooled crust, sprinkle with remaining toasted coconut, and bake until just hot, 6 to 8 minutes. Cool completely, then chill until ready to serve. Cut into six 2 1/3-inch rows; cut rows on a diagonal to form diamonds. Before serving, sprinkle with confectioners' sugar, and garnish with lime zest, if desired.