Place the prepared strawberries in a bowl and add granulated sugar; stir to combine and let them sit for 15 minutes.
Preheat oven to 350ºF while strawberries are macerating.
Using a slotted spoon, place strawberries on a baking sheet lined with parchment paper; keep the juices for later. Transfer to the preheated oven and reduce the heat to 250ºF; roast for 50 minutes.
About 20 minutes later, turn the pan around and roast for another 30 minutes.
When time is up, remove from the heat and toss; return to the oven for 15 minutes and increase the heat to 350ºF for the remaining time.
Remove from the heat and transfer the strawberries and their juices to the bowl of a food processor including the reserved juices; process until smooth, about 15 seconds.
Transfer to a large bowl and add sweetened condensed milk, vanilla extract and fleur de sel; whisk until well blended and set aside.
Make the whipped cream by adding cold heavy cream and powdered sugar to the bowl of a stand mixer. Using the whisk attachment, process until stiff peaks form.
Scoop half of the whipped cream into the strawberry mixture and fold in gently. Add the strawberry mixture to the remaining whipped cream and fold it in until well mixed and fairly smooth.
Pour mixture into a 9x5x3 chilled metal loaf pan, cover with plastic wrap, then with foil; transfer to the freezer until hard, about 6 to 8 hours.