Heat oven to 150C/130C fan/gas 2 and line 6 muffin tin holes with muffin paper cases. Melt the butter, stir in the biscuit crumbs until well mixed, then press as firmly as you can into the bases of each paper case. Chill them while you make the filling.
Beat the ricotta with the sugar, lemon zest and juice, whole egg, egg yolk and vanilla. In another bowl, whisk the cream until it just holds its shape, then fold into the cheese mixture. Spoon evenly into the paper cases, right up to the tops, then tap the tin on the work surface to flatten the filling. Bake for 30 mins, then turn off the oven and allow to cool completely inside.
To decorate, top each cheesecake with 1 tsp jam and a strawberry half.