Step 1 – Preheat the oven to 350°. Butter a 9-inch gratin dish. In a bowl, whisk the flour, sugar and a pinch of salt. Whisk in the eggs, butter and lemon zest until smooth. Add the milk and whisk until light and very smooth, about 3 minutes. Pour the batter into the gratin dish and top with the raspberries.
Step 2 – Bake for about 30 minutes, until the clafoutis is set and golden. Let cool slightly. Dust with confectioners’ sugar, cut into wedges and serve.