Cover the almonds with cold water and leave to soak overnight.
The next day, soak the rice in cold water for at least 30 minutes.
Drain the almonds and purée them thoroughly with a hand blender (or stand mixer) together with 450 ml of water and a pinch of salt until almond milk forms.
Spread a cloth (preferably cheesecloth) in a bowl, pour in the almond milk, and squeeze the cloth thoroughly. Collect the liquid. This is the finished almond milk. I ended up with about 330 ml.
Drain the rice and add it to the almond milk. Blend with a hand blender for about 30 seconds.
Bring the almond milk, rice, butter, and sugar to a boil while stirring. Add the violet blossoms and simmer for about 15 minutes.
Pour into small bowls. Enjoy hot or cold.
