Prepare the Ramekins: Grease each ramekin with butter and coat with a light dusting of sugar. This helps the soufflé rise evenly.

Heat the Milk & Vanilla: In a saucepan, heat the milk with vanilla seeds or extract over medium heat until warm but not boiling. Remove from heat.

Make the Base: In a bowl, whisk together egg yolks, half the sugar, and cornstarch until smooth. Gradually add the warm milk while whisking continuously.

Cook the Mixture: Pour the mixture back into the saucepan and heat on low, stirring constantly, until thickened (about 2 minutes). Remove from heat and let cool slightly.

Beat the Egg Whites: In a clean, dry bowl, whip the egg whites using an electric mixer. Gradually add the remaining sugar while beating until stiff peaks form.

Fold the Egg Whites: Gently fold one-third of the whipped egg whites into the base to lighten it. Carefully fold in the remaining whites, maintaining as much air as possible.

Fill the Ramekins: Spoon the mixture into the prepared ramekins, filling almost to the top. Smooth the surface and run a thumb around the edges for an even rise.

Bake the Soufflés: Place the ramekins on a preheated baking tray in a 375°F (190°C) oven. Bake for 15-20 minutes until puffed and golden.

Serve Immediately: Dust with powdered sugar and serve immediately, as soufflés begin to deflate within minutes.