Preheat the oven to 350F (175C) butter two 9 1/2-inch (24 cm) loaf pans.
Combine the flour and baking powder; set aside.
In the large bowl of an electric mixer, combine the eggs and sugar and mix until well blended.
With the mixer at slow speed, slowly add, in this order: the heavy cream, the flour and baking powder mixture, the melted butter, lemon juice, and lemon zest.
Beat until very smooth. Divide the batter evenly between the loaf pans.
Place the pans in the centre of the oven and bake until golden and a toothpick inserted in the centre comes out clean, about 1 hour.
Remove from the oven and cool in the pans on the rack.
To serve, unmold and cut the loaves into thin slices.
This cake can be stored, for several days and carefully covered with plastic wrap.