First things first, let's get prepped. Preheat your oven to 350°F (175°C). Lightly grease and flour or line an 8x8 inch square pan or a standard loaf pan with parchment paper. This makes getting the finished dessert out so much easier!
Grab your favorite mixing bowl – the biggest one you have will be great. Melt your half cup of unsalted butter. You can do this gently on the stovetop or carefully in the microwave. Pour the melted butter into your bowl.
To the melted butter, add the whole milk, large eggs, and the ¼ cup of freshly squeezed lemon juice. Give these wet ingredients a little whisk to combine them nicely.
Now for the dry stuff! Add the all-purpose flour, granulated sugar, lemon zest, baking powder, and salt right into the same bowl with the wet ingredients.
Using a spatula or a wooden spoon (or even your whisk, cleaning it as you go!), gently mix everything together. Mix just until the dry ingredients are incorporated and you don't see any streaks of flour. Be careful not to overmix – overmixing can lead to a tough texture, and we want tender, moist lemon goodness!
Pour the batter into your prepared pan and spread it out evenly.
Pop the pan into your preheated oven. Baking time will vary slightly depending on your pan size and oven, but for an 8x8 inch pan, it might take around 25-35 minutes, and for a loaf pan, it could be 45-55 minutes. You'll know it's done when a toothpick inserted into the center comes out clean (maybe with a few moist crumbs, but no wet batter).
While your amazing lemon dessert is baking (and making your kitchen smell like heaven!), you can whip up the optional glaze if you like. In a small bowl, whisk together the 1 cup of powdered sugar and the 2 tablespoons of lemon juice until smooth. If it's too thick, add a tiny splash more lemon juice or milk. If it's too thin, add a little more powdered sugar.
Once the dessert is baked, take it out of the oven and let it cool in the pan for about 10-15 minutes before carefully lifting it out (using the parchment paper handles if you used them!) and placing it on a wire rack to cool completely.
Once it's completely cool (this is important, otherwise the glaze will melt!), drizzle the lemon glaze generously over the top. Let the glaze set for a bit before slicing and serving.