I do like Korean isekai, I find the difference of perspective interesting. If this was Japanese she would have made curry instead, how that fits into the tea theme I don't know but it would have happened.
The milk jam in this chapter is not dulce de leche. Korean people usually use fresh milk to make them. It's fresh milk + heavy/whipping cream + sugar
(boil and stir until they're done)
The chapter started with the chef giving the duchess a weird look, and I was sure she was going to do something to sabotage the jam... I'm glad it was the complete opposite! They're all warming up to her. ❤️
And now she will have a huge sucess with her new business, become even more popular than the Duke and take control of the house, firing everyone who don't like her.