Preheat the oven to 200°C.
Peel the pears and cut them in half lengthways. Remove the core with a teaspoon or melon baller. Place the pear halves next to each other on a baking tray on their cut side and cover them in baking paper. Brush the pears with 20 g of the butter and sprinkle them with the granulated sugar. Bake the pears in the oven for 30 minutes. Turn them halfway through. Allow them to cool completely.
Meanwhile, place the syrup, brown sugar and the rest of the butter in a saucepan. Gently heat the mixture until the butter has melted. Stir occasionally. Bring the mixture to the boil and allow to simmer for 5 minutes. Add 75 ml of cream and bring back to the boil. Leave to boil for one more minute and then transfer into a bowl. Allow to cool.
Prepare the crème pâtissière in line with the instructions on the packaging.
Cut the slices of cake in half. Place half of the pear on top with the round side facing down and the cut side against the glass. Place half a slice of cake on the bottom of each glass jar, next to the pear. Then build layers of crème pâtissière, caramel sauce, slice of cake, crème pâtissière and caramel sauce up against the pear. Close the jars and store them in the fridge.
Whip the rest of the cream at the serving location. Open up the jars and serve them with a large dollop of whipped cream on top.