Preheat oven 375 degrees F. Butter a large 9x13 deep casserole dish with butter.
In the bowl of a large stand mixer, beat the room temperature butter and sugar together over medium speed until nice and creamy. Once the sugar and butter are creamed, slowly add the eggs, one at a time. Mix well between each addition. Then add the vanilla, heavy cream and salt. Mix until everything is combined.
Tear 6-8 croissants alternating between tearing in half and in thirds. Place the torn croissants in the buttered casserole dish, top with fresh blueberries (blackberries would also be wonderful) and pour the custard over the top. The custard mixture may appear clumpy, thats ok!
Sprinkle the top with ¼ cup sugar and bake at 375 degrees F for 30-35 minutes.
Serve as is or with whipped cream, maple syrup or powdered sugar! EAT.