Remove pits from medjool dates and put them in a larger bowl. Pour boiling water over them and let them soak for 10 min.
After 10 min take them out and discard the water. Mash them with the back of a fork (the more you will mash them, the less work your blender will have and you'll get a smoother paste).
Put mashed medjool dates in the blender and mix on the lowest speed. Blend for a while until you get a smooth paste. It's fine if you still see some traces of medjool dates in the paste when it's done.
Transfer the medjool date paste into a large bowl. Add peanut butter, salt and vanilla. Mix together.
Add peanut butter powder to the mixture and mix. Mix until you get a filling that doesn't stick to your fingers and then some more.
Divide the filling in 50 equal parts (I measure them in grams) if making normal or king size peanut butter cups or in 125 equal parts if making mini size peanut butter cups. Squash them and shape them into balls.
Chop chocolate into smaller pieces and put it in a double boiler over medium heat to slowly melt.
Take one cup mould and pour a little bit of chocolate onto the bottom. You will need about 4g of chocolate for the normal size cup, about 5g for the king size cup and 2g for the mini size cup. Take a teaspoon and coat the sides with chocolate. Go up to 1.5 cm height for the normal size cup, up to 2 cm for the king size cup and up to 1.6 cm for the mini size cup. Put the mould into the freezer for the chocolate to harden.
Repeat the same process with the rest of moulds.
Take the first mould out of the freezer. Take one ball of the filling, flatten it and put it in the chocolate hole. Tap gently with your fingers (pressing too hard can break the chocolate underneath) so that it fits perfectly into the moulded chocolate. Pour some additional chocolate on top. You will need about 3g for the normal size cup, 4g for the king size cup and 1g for the mini size cup. Rotate the mould so that melted chocolate goes around over the top area. This will make the top look very nice without you needing to touch it with a teaspoon. Then if it's needed correct the sides with a teaspoon and perhaps add a little bit of additional chocolate so that the chocolate covers the sides as well. Sometimes it's enough just to press the sides of the silicone mould against the wet chocolate. Return the mould into the freezer.
Repeat the last step with the rest of the moulds. If at anytime in this process you notice that the chocolate got thicker, melt it again over double boiler.
Take the first mould out of the freezer and take the peanut butter cup out of the mould. Be careful not to leave your fingerprints on the chocolate. Put the peanut butter cup on a plate lined with parchment paper.
Repeat the same with the rest of the moulds in the freezer.
If any of the peanut butter cups have chocolate that was coated too high on the sides, trim them with a knife.
Store the plate with peanut butter cups in the refrigerator.
Take peanut butter cups out of the refrigerator 10 min before eating them so they become softer and more enjoyable to eat.