Combine sugar and flour with one cup of milk at a time.
Cook over low heat, stirring until slightly thickens.
Remove from fire and let cool (covered).
When cool, add 1 teaspoon vanilla, 5 eggs.
Beat with beater until smooth.
Add ½ jigger rum (optional).
Melt 10 tablespoons sugar in tube pan until brown.
Roll sugar around pan, add filling.
Put pan in little water while baking and bake for 1 hour at 350°F.
Turn over when very cool.