Keep a generous handful of the strawberries whole, with stalks on, to decorate the finished dessert.
Remove the stalks from the rest of the strawberries. Place a saucepan over medium heat and add half of these strawberries to the pan. Sprinkle over the sugar and water and allow to cook for 3-4 minutes until the fruit is soft enough to crush lightly with a fork. Set aside to cool for 10 minutes.
Cut the remaining strawberries in half and place in a bowl, pour over the cooked strawberries in the pan and scatter over the lemon verbena leaves. Mix well and leave to one side.
In a clean bowl, whisk the mascarpone and cream together to form soft but firm peaks.
Brush a bowl or pudding basin with the oil, then line with cling film, overlapping it so the whole inside is well covered. Make sure the cling film overhangs the edges of the bowl by about 10cms all around.
Cut the brioche into 1 cm thick slices and use to line the prepared bowl, doing the sides first, then the bottom and slightly overlapping each slice. Gently press two large spoonfuls of the strawberry mix into the base of the mould, then add a couple of spoonfuls of the mascarpone mixture, spreading it flat.
Repeat the layer until the bowl is full then top with the remaining brioche slices, completely covering the filling. Fold over the excess cling film, pressing down gently.
To serve: fold back the cling film, place a serving plate upside down over the bowl and
carefully invert onto the plate. Carefully lift the bowl away, holding the edges of the cling film if necessary, to un-mould. Remove the cling film and scatter the reserved strawberries over the top and around the edges.