Preheat your oven to 350°F and grease a 9 by 5 inch loaf pan. Line with parchment for easy removal.

Cream the softened butter with granulated sugar until pale and fluffy, about 2 to 3 minutes.

Beat in the condensed milk until the mixture looks glossy and smooth.

Add the eggs one at a time, mixing well after each addition.

Stir in the lemon zest and vanilla extract.

In a separate bowl, whisk together the all-purpose flour, baking powder, and salt.

Mix the dry ingredients into the wet ingredients in two additions.

Finally, add the lemon juice and stir until just combined. If the batter seems thick, add a teaspoon of milk to loosen it up.

Spoon the batter into the prepared loaf pan and smooth the top.

Bake for 45 to 55 minutes, or until a toothpick inserted comes out with moist crumbs.

Cool in the pan for 10 minutes, then lift onto a wire rack.

To make the drizzle, stir the condensed milk with lemon juice and a pinch of salt until pourable.

Poke tiny holes in the warm cake with a skewer, then pour the drizzle slowly so it sinks in.

If using optional frosting, once cooled and set, spread a thin layer of lemon buttercream over the cake.

Rest the cake for 20 minutes before slicing to keep the crumb neat and help the drizzle settle.