Caramelization on cake

Hello. I need a bit if help. My grandma use to make the best pineapple upside down cake before she passed. I'll attach her recipe below. But what I can't figure out is this. When she would make the cake, the top where the brown sugar is, would be hardened, like caramelized or whatever. But every single time I make it, it just comes out soft. I'm not sure if I'm using too much sugar or not enough butter or what, I've also tried flipping it both as soon as it comes out of the oven and also after it cools. I've tried putting the sugar in when the butter is piping hot and even putting it back in the oven for a bit before putting the cake mix in top of it. Idk what to do. Please help?

Grams Pineapple Upside down cake

Box of cake mix(for pineapple cake)

1) Can of pineapple (save the juice)

2) Brown sugar both light and dark

3) ¼ spoon of butter

Oven temp should be according to cake mix

Melt butter in pan

Spread sugar all over bottom of pan

Spread pineapple on sugar (should take whole can)

Use the pineapple juice in cake recipe instead of water

When cake is done immediately flip over

Vole: you have dessert for the gang