Pour fresh lemon juice into the blender.
Add honey or simple syrup to the lemon juice, then pulse briefly to combine and dissolve the sweetener, releasing a bright citrus aroma.
Add the crushed ice to the blender, filling it up over the liquid ingredients.
Secure the lid on the blender and blend on high until the mixture is smooth, icy, and frosty looking, with no large ice chunks remaining.
Check the consistency — it should look snowy and feel thick but pourable, with a vibrant lemon color.
Pour the chilled lemonade slushie into glasses, letting it mound slightly as it begins to melt a bit around the edges.
Serve immediately with a straw or a small spoon, enjoying the icy, tangy refreshment.