Pour the fresh lemon juice into the blender, followed by the sweetener, ensuring it dissolves well.
Add the crushed ice into the blender, filling it up to the top for a thick, icy texture.
Drop in the surprise ingredient — whether it's flavored jam, a splash of soda, or syrup — to give the slushie a fun, unexpected twist.
Secure the lid on the blender and blend on high until the mixture is smooth and slushy, with a thick but pourable texture.
Check the consistency; it should be icy yet scoopable, with no large ice chunks remaining.
Pour the bright, icy lemonade into glasses, ensuring each servings has a well-mixed pop of flavor.
Insert a straw and serve immediately for a refreshing, playful treat.