Why does my "dulce de leche" look like this? So I tried making dulce de leche, I've poured
1.5 litres of milk, 500g sugar and a teaspoon of vanilla extract.

I've waited for it to create foam that'll touch the rims and made sure the sugar is dissolved.

I lowered the heat and kept on stirring.

it's important to mention that I did not see at any given time that it went to the brownish color with the actual dulce de leche texture. 

It felt like it went from beige to burnt brown without anything in between.

does anyone know why it happend?
I tried it again with fewer amounts and it came out perfectly (also added baking soda) as I also waited the right amount of time after it turned brown(i think it was about 5-10 mins).
and constantly took a sample to see how thick it is.
thanks for your help!