Preheat the oven to 400 F (200 C).Cream the butter with the sugar until the mixture is smooth and light.Add the eggs one by one, beating well between each addition. The mixture will be pale yellow and creamy.Add the buttermilk, vanilla extract, lemon juice, and lemon zest, and 1 cup (100 g) of shredded coconut. Mix well.Pour the preparation into the pre-baked tart shell.Sprinkle with the remaining coconut.Bake for 10 minutes, then reduce the temperature to 350 F (180 C) and continue baking for 35 to 40 minutes, until the top of the tart has a dark caramel color.Let cool on a rack before cutting into slices and serving with ice cream.