Brushing lemon simple syrup onto the cake helps keep it moist. Martha made this bundt cake recipe on episode 506 of Martha Bakes.
Preheat oven to 325 degrees. Butter a 12-cup Bundt pan; dust with flour, tapping out excess. In a medium bowl, sift together flour, baking powder, and salt.
In a mixing bowl, beat butter on medium-high until pale and fluffy, about 2 minutes. Add 1 1/2 cups granulated sugar and lemon zest; beat until light and fluffy, about 5 minutes. Beat in eggs, one at a time, scraping down sides of bowl. Reduce speed to low; beat in flour mixture in three additions, alternating with two batches coconut cream, until just combined (do not overmix).
Transfer batter to prepared pan; tap on counter, and smooth top with an offset spatula. Bake until golden brown and a cake tester comes out clean, about 45 minutes.
Meanwhile, in a small bowl, make lemon syrup: combine the lemon juice (you will need about 1/3 cup), remaining 1/4 cup granulated sugar, and 1/2 cup water. Stir until sugar is dissolved.
Transfer Bundt pan to a wire rack to cool 30 minutes. Gradually brush cake with lemon syrup over the next 30 minutes as it continues to cool, letting it absorb before brushing on more. Turn out cake onto rack to cool completely. (Cake can be stored at room temperature, wrapped in plastic, up to 3 days.)
In a well-chilled bowl, whisk heavy cream until soft peaks form. Add confectioners' sugar and whisk until medium-stiff peaks form. Just before serving, top cake with whipped cream, then toasted coconut.