Flour glue is amazing stuff. It's super sturdy, almost nothing to make and if you let it get really concentrated, it's pretty much wheat paste.
The basic ratio for the kind of flour glue I make is 1 part flour to 2 to 4 parts water, mixed and added to 20 parts boiling water.
So, first, get your 20 parts (for this case, 2.5 cups) water boiling in your saucepan.
Mix the flour and 1/2 cup water. A fork works well to properly mix the flour and tap water
Once your pot is boiling, take it off the heat and add the water/flour mix from earlier.
Stir well. You need to take it off the heat when doing this, or you end up making dumplings.
Return to heat and simmer your flour glue until it is a snot-like consistency. Let cool to bathwater temperature and then use. It works best when warm, so store leftover in the fridge and warm it back up in a saucepan when you need it again. Adding cloves or oil of cloves will keep it lasting longer.