In a heatproof bowl placed over a pan with gently simmering water melt together butter and chocolate.
Remove the bowl from the heat and add in the cracker crumbs (crushed in a zipped bag with a rolling pin or in a food processor). Mix until well combined.
Press the prepared crust onto the bottom of a 7 inch/ 18 cm springform pan lined with parchment paper. Let the pan sit in the fridge while preparing the cheesecake filling.
In a small saucepan over medium heat combine chopped strawberries and sugar and bring to boil. Let simmer for about 30 minutes, mixing from time to time. When the mixture starts getting thick, remove from heat and let cool until room temperature.
In a large mixing bowl whip the sour cream with vanilla and powdered sugar for 5 minutes at high speed. Add cream cheese and beat at a lower speed until well combined.
Combine the gelatine with the water. Let sit for 5-10 minutes to bloom.
Place the gelatine with the water in a small heatproof bowl over a pan with gently simmering water (double boiler). Whisk continuously until the gelatine is completely dissolved.
With the mixer on high speed, slowly add the gelatine mixture to the cheesecake filling. Beat until combined very well.
Assemble the cheesecake:
Spoon a small part of the white filling in the prepared pan, over the crust. Place the pan in the fridge.
Add about ⅓ of the strawberry mixture to the remaining filling in the bowl. aMix with a spatula until well combined.
Spoon some of of the coloured filling in the pan to cover completely the white one.
Add about half of the remaining strawberry mix to the cheesecake filling and mix until well combined. Spoon another layer of filling into the pan (it should be slightly more intensive pink than the previous layer).
Add the rest of the strawberry mix to the cheesecake. Mix well until combined. Pour/ spoon the rest of the strawberry filling into the pan. Smooth out the top with the spatula.
Cover the cheesecake with cling film and let stay in the fridge for at least 6 hours.