Prep. Preheat oven to 350℉ with the rack in the center. Wait to grease the Bundt pan until you are ready to pour the batter in. This will prevent the grease from pooling, creating uneven spots.
Beat butter and sugar. Beat butter and sugar using an electric mixer for 3 to 5 minutes, until light and fluffy. The color of the butter will change when it has been beaten enough. Add the eggs, one at a time, and beat each in until well combined. Add the coconut extract.
Finish batter. Combine the flour, baking powder, and salt in a separate large mixing bowl. Add to the butter mixture, alternating with the milk, one-third at a time, mixing on low until just combined. Do not overbeat. Stir in the lemon juice and lemon zest by hand. Prepare a 10 or 12-cup Bundt pan by generously spraying with cooking spray or coating with shortening and dusting with flour. Pour the cake batter immediately into the pan and smooth the top.
Bake. Bake for 45-55 minutes until a cake tester inserted into the center comes out clean. Allow the cake to cool in the pan for about 10 minutes, then carefully flip onto a wire cooling rack. Once the cake has cooled, make the frosting.
Frost and garnish. Combine the powdered sugar and lemon juice in a small bowl and mix until it is smooth. The icing should be thick and barely pourable. Pour onto the very top of the cake and allow the icing to settle down the sides of the cake. Sprinkle the flaked coconut on top before the icing sets. Cake will keep tightly covered at room temperature for at least 2 days.