The base of your block mold needs to be 1 ½” wider than the bowl. So first trace the bowl onto the foam board and then measure ¾” past the bowl on each side.
Use hot glue (or 100% silicone caulk) to attach the sides to the base. Gluing it first will make it easier to work with when you go to tape it.
To create a drainage hole, cut a jumbo drinking straw to about 2” taller than the inside height of the bowl. Then glue it to the center and take care that the straw is secure.
Fill a measuring glass with water and let’s say it is a 32oz glass. Pour that into the pitcher and use a permanent marker to mark this on the pitcher.
To remove the concrete silicone mold from the form, use a utility knife to cut through the taped areas and between the foam board pieces where it’s glued.