Preheat oven to 350°F (177°C). Line an 8 x 4 inch loaf pan with parchment paper.
Add flour and sugar to a large mixing bowl. Whisk until evenly combined. Then perform a quick sift of your mixture by running your whisk rapidly back and forth through the flour until there are no visible lumps of flour. Do not actually sift the flour in (through a sifter or a mesh strainer). The goal is just to do a quick sift to break up any clumps so that you can easily mix the batter without overmixing it.
Add in lemonade and butter. Whisk until your batter is smooth and no flour lumps remain.
Add batter to your prepared loaf pan. Bake for about 40 minutes or until the edges of the cake are lightly browned and toothpick inserted comes out clean.
Notes
This cake does not bake up that high. Each slice will be about 2 inches in height if baked in an 8 x 4 inch loaf pan with slanted edges. A pan with slanted edges measures 8 x 4 on the top but is less around the base (around 7.5 x 3.5 inches). If you have a pan with straight edges your cake will bake up shorter.
I don't recommend increasing the amounts to get a taller cake. The recipe as is will rise almost to the top of the cake pan. If you increase the ingredient amounts and the cake rises above the pan, the batter that bakes above the edge of the pan will actually spread more to the side of the pan instead of baking up (like a muffin top).
You can also bake in an 9 x 5 pan but your cake will be very short and you will need to cut down on baking time.
I used Simply Lemonade. I don't recommend using low-sugar lemonade as your cake may not be sweet enough.
The reason for doing a quick sift of the dry ingredients is to allow you to easily mix the batter. If you don't do a quick sift first, you may end up with some lumps of flour in your batter that are difficult to break up with just a whisk or you have to mix the batter much longer to try to get those lumps out which results in the batter being overmixed.
To properly measure flour, spoon the flour into the measuring cup and then level off with a knife. Do not directly dip the measuring cup into the flour because this results in too much flour. Use this method of measuring whether you are measuring self-rising flour or measuring all purpose flour to make your own self-rising flour.
Self-Rising Flour: To make your own self-rising flour, whisk together 2 cups all purpose flour, 3 tsp baking powder and 1/2 tsp salt to a bowl. Measure out 1 3/4 cups for the recipe.
Lemon Glaze: Add 1 cup of powdered sugar to a medium bowl. Whisk in 1 tbsp of lemon juice. If you find the glaze too thick you can add in a little more lemon juice to thin it out but I found 1 tbsp to be just right. You can also stir in 1 tsp of fresh lemon zest to the glaze or add the zest after glazing the cake. I added the zest on top after glazing the loaf.
The nutrition information provided are only estimates based on an online nutritional calculator. This is not a comprehensive list of all the nutrients in the recipe (i.e., does not include vitamins, cholesterol, etc). I am not a certified nutritionist. Please consult a nutritionist or doctor for accurate information and any dietary restrictions and concerns you may have.