Preheat your oven to 350°F (175°C) and generously butter a 9-inch pie dish.

In a large bowl, whisk together 3 large eggs until frothy. Gradually add sugar, flour, and salt, then mix in whole milk, heavy cream, and vanilla until smooth.

Spread blackberries across the bottom of the prepared dish, then pour the batter evenly over them.

Bake in the preheated oven for 35 to 40 minutes until the top is puffed and golden.

Let cool on a wire rack for about 10 minutes, then dust with powdered sugar before serving.