Roughly break the plain biscuits and blend them in a food processor together with the soft butter. Butter the inside of four 9 cm diameter pastry rings, line them with a strip of baking paper (or better yet, acetate) and place them directly onto small plates. Alternatively, you can use glass tumblers or ceramic ramekins. Divide the biscuit base among the pastry rings, press down using the back of a teaspoon and place in the fridge.
Peel 3 peaches (you should end up with about 500 g of prepared flesh), remove the stone and cut them into cubes. Transfer them to a saucepan, drizzle with the lemon juice, add the sugar and cook over a medium heat for about 15 minutes, until they are soft enough to almost form a cream. Blend the purée in a food processor, transfer it to a bowl and place it in the fridge, covered with cling film, until ready to use.
In a bowl, cream the ricotta and spreadable cheese with the icing sugar. Take 1/3 of the peach purée and fold it into the cream.
Divide the prepared cream by spooning it into the pastry rings, over the biscuit bases, and leave the cheesecakes to set in the fridge for at least 5 hours.
When ready to serve, carefully unmould the pastry rings, remove the strip of baking paper and decorate each cheesecake by spreading the remaining peach purée over the surface and arranging a few slices of fresh peach on top. Finish with a few sprigs of thyme and serve.
If you used glasses or ramekins, you won't need to unmould the cheesecakes.
