In a large bowl or electric mixer, whisk together the flour, sugar, baking powder, baking soda and salt. Using the electric mixer, mix in cubed butter until it's the size of small walnuts. Stir in the cream until the flour is just moistened and the dough starts to come together in large clumps. Stir in the lemon zest and poppyseeds. Knead the dough in the bowl just until it holds together, and turn it out onto a lightly floured board.