Blend your plant milk, condensed milk, and pumpkin spice until smooth (I used my magic bullet for this -- smaller and faster to clean up...). Set aside for about 10 minutes, then blend again.
Fill a cup with ice to the top.
Pour the coffee in, filling it roughly half way (saving a bit of the coffee for a later step).
Pour the condensed milk mixture in, leaving a bit of room at the top.
Pour more of the coffee into the cup over the back of a spoon (see photos and explanation above) until filled all the way.