Make the Loaf: Preheat oven to 350 degrees F. Grease an 8x4-inch loaf pan and line with parchment paper.
Using an electric mixer on medium speed, beat the butter, sugar and lemon zest until pale and fluffy, about 3 minutes. Add the eggs one at a time, adding a pinch of the flour with each egg, beating well after each addition.
Sift the remaining flour, baking powder and baking soda into the batter. Use a rubber spatula to fold the flour mixture into the batter. Add the hot water, ground almonds and poppy seeds and gently stir together with the spatula. Transfer the mixture into the prepared pan and bake until a skewer inserted into the center comes out clean, 40 to 50 minutes. Place on a wire rack to cool for 20 minutes.
Make the Drizzle: In a small saucepan over low heat, stir together the superfine sugar and lemon juice until the sugar has dissolved.
Turn the cake out of the pan and poke the top of the cake all over with a skewer. Slowly spoon over about three-quarters of the lemon syrup. Allow the cake to cool completely.
Once cool, sprinkle the granulated sugar all over the top of the cake. Reheat the remaining syrup, if necessary, then drizzle over the sugar. Serve at room temperature. The cake can be stored at room temperature, wrapped in plastic wrap, for up to 4 days.