Measure out freshly brewed coffee and let it cool to room temperature to prevent melting the ice too quickly.
Add the cooled coffee to the blender, then pour in the heavy cream and sprinkle in the sugar and vanilla extract if using.
Place the ice cubes into the blender and secure the lid tightly.
Blend on high speed for about 30-40 seconds until the mixture is thick, frosty, and smooth, with no large ice chunks remaining.
Stop the blender and check the consistency; if it’s too thick, add a splash of milk or coffee and blend briefly to loosen it slightly.
Pour the frosty coffee slushie into glasses, allowing the icy beverage to mound slightly above the rim for a generous presentation.
Garnish with whipped cream or a dusting of cocoa powder if desired, then serve immediately with a straw or spoon for optimal enjoyment.