Key Lime Coconut Cake

Directions

1. 1
   Preheat oven to 350°F with rack in middle. Generously butter a 9- by 2-inch round cake pan and line bottom with a round of parchment paper.
2. 2
   Toast coconut in a small baking pan in oven, stirring once or twice, until golden, 8 to 12 minutes. Cool. Leave oven on.
3. 3
   Beat together butter, granulated sugar, and zest with an electric mixer until fluffy. Beat in eggs 1 at a time. Stir together flour and 1/2 cup coconut (reserve remainder for topping). Stir together milk and 2 Tbsp lime juice. At low speed, mix flour and milk mixtures into egg mixture alternately in batches, beginning and ending with flour.
4. 4
   Spoon batter into pan and smooth top. Bake until golden and a wooden pick inserted into center comes out clean, 40 to 45 minutes. Cool to warm, then turn out of pan and discard parchment.
5. 5
   Whisk together confectioners sugar, remaining 2 Tbsp lime juice, and rum (if using) and pour over cake. Sprinkle with remaining coconut.