freshly squeezed lime juiceto taste (to make sour cream)
Soak the almonds for a couple of hours or until they plump up and become softer, drain before using. Place all the almonds and only half of the water into the blender and blend for a couple of minutes.
Add all the cornstarch, a little bit (like a pinch) of salt, the other half of the water and blend until completely smooth -- the time will depend on the power of your blender. If you're blender isn't too powerful you may want to pass the liquid through a fine sieve to catch any bits and prevent a grainy crema.
Over medium heat cook the mixture until it thickens. This will take about 10 minutes. It's very important that you keep stirring the whole time to prevent it burning or bubbling over. As it cooks you'll notice that little by little the cream begins to form as the mixture thickens. You'll know that the crema is ready when it has a thick creamy consistency. When ready, remove from heat and allow to cool for a few minutes while you keep stirring it.
At this time if you want a more neutral tasting crema you can simply leave as is and cool completely before storing. For a more tart cream continue with the next step.
To make the "sour" cream
Once allowed to cool slightly, little by little add freshly squeezed lime juice and salt to the cream. Stir until well combined, allow to sit a couple of minutes, then taste and if needed add a bit more lime juice and/or salt until you get the tartness you're happy with.
Pour into a container and if serving it right away allow to cool a bit more, otherwise store in the fridge covered for up to 4 days. Enjoy it over all of your favourite Mexican dishes, or as desired.
*Watch the almond blanching tutorial here, How to Blanch Almonds **Longer soaking time will only be required if your blender isn't too powerful, otherwise the almonds may not breakdown enough and you'll have to strain the liquid through a fine sieve before cooking. So to soak the almonds, after blanching cover in room temperature water and all to soak for a couple of hours or until soft.