Combine warm milk and active dry yeast in a bowl, letting it sit for about 5 minutes until it becomes foamy.

Mix together the flour, salt, sugar, and cornstarch in a large mixing bowl until evenly combined.

Add the yeast mixture, vegetable oil, and eggs to the dry ingredients, and mix until a smooth dough begins to form.

Knead the dough on a floured surface for about 8-10 minutes until it feels smooth and elastic.

Place the kneaded dough in a greased bowl, cover it, and let it rise in a warm space for about 1 hour.

Prepare the filling by gently heating the milk, condensed milk, and vanilla extract in a saucepan.

Roll out the dough on a floured surface, cut it into pieces, fill each with the creamy mixture, and seal securely.

Shape the filled pieces into round buns and place them on a baking sheet lined with parchment paper.

Brush the tops of the buns with milk, and allow them to rise again for about 30 minutes.

Bake in a preheated oven at 350°F (175°C) for approximately 20 minutes, or until golden brown.