Make Marshmallows: In a small bowl, soften the gelatin by stirring it into 1/4 cup of the water. Set aside. In a small saucepan
, fitted with a candy thermometer
, bring the remaining 1/4 cup of water, a 1/4 cup of corn syrup, and the sugar
to 240 degrees F (soft ball stage).
In the meantime, put the remaining 1/4 cup of corn syrup
, vanilla, and rum in the bowl of an electric mixer
fitted with the whisk attachment. Add the hot syrup to the bowl and whisk
at high speed for 3 to 5 minutes until thickened. Set the gelatin
over simmering water to melt
. Add the gelatin to the syrup and continue whisking for 6 more minutes until white, fluffy and stiffened.
Top the casserole with a layer of marshmallow
and bake at 350 degrees for 20 minutes, until heated through and browned on top.
Cook's Note: Got extra marshmallow? This should be your biggest problem. Spread a 1/8-inch coating of all-purpose flour
on a baking sheet. Pipe out 1-inch rounds of marshmallow onto the flour. They will spread a little, so leave room. The marshmallows will be set in 20 minutes. Marshmallows are sticky. Dip your fingers in flour before handling.