Peel the bananas and break them into chunks (if frozen, let sit 2–3 minutes to loosen or tap the banana on a cutting board to break into pieces that fit the blender).
If using the espresso beans, coarsely grind or crush them (spice grinder, mortar and pestle, or pulse briefly in the blender).
Lightly crush the cardamom seeds (mortar and pestle, spice grinder, or press with the back of a spoon) to release their aroma.
Pour the soy milk and coconut milk into the blender first.
Add the banana chunks, pitted dates, crushed cardamom seeds, cinnamon, nutmeg, and the prepared espresso beans (if using) to the blender.
Blend on high until completely smooth, stopping once or twice to scrape down the sides and to ensure any spices or beans are fully incorporated (about 30–60 seconds, depending on your blender).
Pour into glasses and serve immediately.