Prepare your pan by greasing generously with oil and sifting icing sugar all over. Tap off the excess. A 5 x 5 Â square pan works well for good sized marshmallows for candy, I used an 8 x 8 here as I wanted mini marshmallows for baking recipes.
Mix the gelatin into the quarter cup of cold water. This is called blooming.
In a thick bottomed sauce pan, measure out another 1/4 cup water and the one cup sugar. Heat until all the sugar dissolves. Swirl or stir so that nothing burns.
Once the sugar dissolves, let it continue heating on low or medium until it reaches soft ball stage. If you have a thermometer, it should register 240 F or 115 C.
If you don't have a thermometer , use a teaspoon and drop little bits of the sugar solution into a cup of cold water. Roll in your fingers. If it forms a "soft ball" , its the right stage. If its not reached the required temperature yet, you will not be able to form a ball with it.
It sounds more complicated than it really is. Basically , if you let all the sugar melt and heat it for a minute or so more - before it turns yellow or amber colour - you should be good.
Once you have reached this stage , immediately take the saucepan off the heat. Mix in the gelatine and stir until dissolved.
Add the vanilla and salt.
If you see undissolved bits , you can strain it now .
Beat with your electric mixer at medium high for few minutes. You want a batter that is white , fluffy and viscus . When you lift the beater or tilt your pan, it should flow slowly. It will be really sticky.
Add your food colour if using ( drop by drop) and beat until incorporated
Using a rubber or silicon spatula , spread the mixture on your prepared pan and smoothen quickly. Rest for atleast 2 hours or overnight .
Remove the marshmallow slab , using a rubber or silicon spatula to nudge it off the sides and bottom.
Dust the top of the marshmallows , your knife and the cutting board with sifted icing sugar. Cut into squares. Dust with icing sugar.