Preheat your oven to 340°F (170°C). Grease a loaf pan with butter and then line it with parchment paper. In a large mixing bowl, use medium speed of the hand mixer to whip softened butter for about 3 minutes until it turns pale and fluffy. In a separate bowl, combine lemon zest and powdered sugar, gently rub with clean hands until well combined.
Add the lemon zest sugar mixture to the butter and stir with a spatula until all dry sugar is incorporated. Then, use a hand mixer to whip the softened butter and granulated sugar until achieving a light and fluffy consistency.
In another bowl, whisk 5 room temperature eggs until they are uniformly mixed. Gradually incorporate the egg mixture into the butter, adding 2 tbsps at a time, mixing well with the hand mixer after each addition.
Pour in the heavy whipping cream, vanilla extract, and lemon juice.
In a separate bowl, whisk together the flour, baking powder, and salt.
Add the dry ingredients to the butter egg mixture. Use the lowest speed setting of the hand mixer to mix just until combined.
Pour the batter into the prepared loaf pan and smooth the top. Fill a piping bag with approximately 1 tablespoon of softened butter. Cut a small opening, around 2 mm in diameter, at the tip of the piping bag. Hover the piping bag above the cake batter and draw a horizontal line across the center. (This step is optional, but it can help with forming an even and perfect crack on the surface of the pound cake.)
Bake in the oven for about 60 minutes, or until a toothpick inserted into the center of the cake comes out clean.
While the cake is baking, prepare the lemon syrup: Combine water and granulated sugar in a small saucepan. Bring the mixture to a boil, and stir until the sugar is completely dissolved. Turn off the heat, then pour the lemon juice into the saucepan, stir until well mixed. Set it aside.
Once baked, remove the cake from the oven, and carefully transfer it to a plate.
When the cake is warm to the touch but not hot, use a brush to gently brush the lemon syrup over the cake's top and sides.
Once the syrup has been absorbed, allow it to soak into the cake for a few minutes, and let the cake to cool naturally.
While the cake is cooling, prepare the lemon glaze: In a bowl, whisk together the powdered sugar and lemon juice until smooth. Once the cake is completely cool, apply the lemon glaze over the top.
Optionally decorate the lemon pound cake with lemon/lime zest and lemon slices. Slice and serve immediately.