Heat oven to 180C/160C fan/gas 4.
Put potatoes, fennel, and garlic in a medium non-stick pan.
Pour in milk and double cream, season well and simmer gently, covered, for 10 mins, stirring halfway through, until potatoes are just tender.
Divide the mixture between 2 small (about 150ml) buttered ramekins and scatter with Parmesan.
Bake for 40 mins until the potatoes are golden and tender when pierced with a knife.
Snip the reserved fennel fronds over before serving.