The trick here is to find the mix of cream/ milk you like. More cream = harder, more milk = softer, but use at least 200ml cream. Here I am using 240ml cream and 260ml milk.
Pour the cream and sugar into a pan (not the milk!)
Add your flavour and then bring to a boil. Don't worry too much about how much flavouring you use at this point. I am using approx 60g of toffee popcorn here.
When boiling, stir to make sure the sugar is dissolved and then leave to cool and infuse.
It infuses a bit like tea - generally the longer the flavour stays in, the stronger the taste - leave for one hour to overnight until you are happy with the smell/taste.
When you're ready, heat it up again (still no milk). When its boiling, take it off the heat, strain through a sieve, and onto the egg yolks.
Stir quickly to mix it all together before the yolks cook. Finally add the milk and leave to cool.
Pour into an ice cream maker and churn for 25-35 mins. Pop in the freezer and it's done! If you churn by hand, stir, pop in the freezer and stir every half hour until it hardens.
For some flavours, cut or chop them to release their flavour. E.g. Herbs - tear roughly with your hands or chop with a knife. With hard things eg coffee, use a hand blender to roughly chop the beans.
For ideas, look at posh restaurant menus (search online) and be inspired! More of your flavour will make it stronger, less will be weaker. Practice to find how strong you like your chosen flavours.
Some ideas - earl grey tea, coffee, cinnamon (try with apple pie), black pepper (try with strawberries), basil, white chocolate & lavender - the choice is limitless!