- With the rack in the middle position, preheat the oven to 180 °C (350 °F). Line the bottom of a 20-cm (8-inch) springform pan with parchment paper. Butter the sides.
- In a bowl, combine the flour and baking powder. Set aside.
- In another bowl, cream the butter and sugar with an electric mixer. Add the egg and beat until smooth. At low speed, add the dry ingredients. Spread into the pan and bake for about 15 minutes or until a toothpick inserted in the centre of the cake comes out clean. Cool completely.
- Line the inside wall of the pan with a strip of parchment paper. Set aside.
- In a bowl, sprinkle the gelatin on the water and let bloom for 5 minutes. Set aside.
- In a saucepan, bring the milk to a boil. Set aside.
- In a bowl, beat the egg yolks and sugar with a whisk. Gradually whisk in the warm milk. Pour the mixture back into the same saucepan and cook over low heat, stirring constantly with a wooden spoon, until the custard coats the back of the spoon. Add the gelatin and whisk until completely dissolved. Set aside.
- In a food processor or blender, purée the strawberries and lemon juice until smooth. Pass through a fine sieve, if desired. Stir in the custard and let cool.
- In a bowl, whip the cream until soft peaks form. Fold the whipped cream into the strawberry mixture. Pour on the cake. Invert a plate over the pan to prevent the surface of the Bavarian to dry. Refrigerate for 8 hours or overnight.
- In a food processor or blender, purée the strawberries and sugar until smooth. Strain.
- Unmould the bavarian and remove the parchment paper. Serve with strawberry coulis and garnish with the diced strawberries. Store in the refrigerator.