In a mixing bowl, combine flour, sugar, and yeast.

Add warm water and vegetable oil, and mix until a dough forms.

Knead the dough for about 10 minutes until smooth.

Let the dough rise in a warm place for 1 hour.

In a bowl, mix sweetened condensed milk and sugar until well combined.

Divide the dough into small pieces and flatten each piece.

Place a spoonful of filling in the center and fold the dough over to seal.

Place the buns in a steamer and steam for 15 minutes.