Brew a cup of coffee and let it cool to room temperature. Measuring the coffee in a cup will help you gauge the amount needed for blending.
Pour the cooled coffee into a blender, then add the sweetened condensed milk for a rich sweetness and creaminess.
Sprinkle a pinch of sea salt into the mixture to elevate the flavors and add a subtle savory note.
Add the ice cubes to the blender, creating a mound that surrounds the liquid ingredients.
Secure the lid on the blender and pulse the mixture a few times to start crushing the ice.
Blend on high until the mixture is smooth, thick, and slushy, with a frosty appearance.
Stop the blender and check the texture; it should be creamy and icy, with visible ice crystals but no large chunks.
Pour the coffee slushie into chilled glasses, allowing the silky, frosty texture to shine through.
If desired, garnish with a light sprinkle of cocoa powder or a coffee bean for presentation.
Serve immediately with a straw or spoon, enjoying the cool, creamy, and invigorating flavors of the coffee slushie.