I figured out an easy way to make use of the still-delicious-smelling end of candles, once the wick burns out.
dedicated ice cube tray
a way to melt the wax
tart warmer so you can melt your tarts
Step 1: Melt the Wax
Melt the wax. You can use a candle warmer (same as a coffee cup warmer), or the burner of a drip coffee pot.
Wax smoke is bad for you. Wax can catch fire. Don't heat too hot. Use a double-boiler if you have to use the stove.
Step 2: Pour Wax Into Ice Cube Tray
Pour the melted wax into a dedicated ice cube tray. The smell will permeate the tray, so you won't want to make ice cubes in it any more.
You may want to put newspaper under the tray to catch drips; but wax comes off hard surfaces pretty easily, so don't worry too much.
A 14 cube tray can hold the ends of 2 or 3 large jar candles. So you may want to wait til you have a couple ready before making tarts.
Step 3: Allow Wax to Cool
I let the wax set for about 15 minutes on the counter. That way the wax doesn't splash out when you move the tray. Transfer the semi-set wax cube tray to the freezer to harden. The wax needs about 20 minutes to cool in the freezer.
Step 4: Crack the Tarts Out
Now that the wax is cool in the tray, twist the tray as you would to get ice out. The wax won't pop out, but it easily slides out when you turn the tray upside down.
Step 5: Tarts!
There you have them! Put them in a tart or oil warmer to melt.
The ice cube tray will clean easily, but the smell won't disappear. Keep the tray for next time!