Prepare your strawberries by washing them thoroughly under cold water and removing the green hulls with a paring knife. If using fresh strawberries, cut them in half to help them blend more easily and release their natural juices.
Add the strawberries to your blender first, followed by the granulated sugar. This order helps the sugar start dissolving into the strawberry juices immediately, creating a sweeter base for your slush.
Pour in the cold water and fresh lemon juice over the strawberries and sugar. The lemon juice brightens the strawberry flavor and adds that signature tangy note that makes Sonic slushes so addictive.
Add the ice cubes on top of the liquid ingredients in the blender. Using this layering method ensures the blades can grab the liquid first and create a vortex that pulls the ice down for even blending.
Blend on high speed for 30-45 seconds, stopping to scrape down the sides if needed. You want a slushy consistency where the ice is finely crushed but not completely liquified - it should be thick enough to drink through a straw but still pourable.
Add the lemon-lime soda to the blender and pulse 2-3 times just to incorporate. This adds a subtle fizzy sweetness and helps achieve that authentic Sonic flavor without over-blending, which would flatten the carbonation.
Taste your slush and adjust sweetness if needed by adding more sugar, one tablespoon at a time, and pulsing briefly to mix. The sweetness should be bold and candy-like, similar to what you'd get at the drive-in.
Pour immediately into a large glass and serve with a wide straw for the best sipping experience. The slush will begin to melt within 10-15 minutes, so enjoy it right away for that perfect icy texture that makes Sonic slushes so refreshing.
