Preheat the oven to 300°F (150°C) and position a rack in the middle of the oven.

In a medium bowl, mix 2 cups all-purpose flour with 3/4 teaspoon baking powder. Set this dry mixture aside.

In a small bowl, combine 1/2 cup milk with 1 teaspoon vanilla extract. Set aside.

In a large bowl, beat 1/2 cup salted butter (room temperature) with 3 tablespoons brown sugar until the butter is lighter in color and the mixture is fluffy.

Add the dry flour mixture and the milk mixture to the butter mixture alternately, beginning and ending with the flour, and mix just until a soft, workable dough forms.

Lightly dust a clean work surface with extra flour. Turn the dough out onto the surface and dust the top with a little flour. Use a rolling pin to roll the dough thin and even.

Cut the rolled dough into 4" x 4" (10 cm x 10 cm) squares.

Place about 1 teaspoon of guava paste near one edge of each square. Roll the square from that edge toward the opposite edge to enclose the filling, pinching the seam and the ends to seal. Place each roll seam-side down on a baking sheet, spaced so they do not touch.

Bake in the preheated oven for 20 minutes, until the biscuits are set.

While still hot, coat each biscuit with powdered white sugar: either roll them in a shallow dish of the 1 cup powdered sugar or sprinkle the sugar over them with a spoon so they are evenly coated.

Cool the biscuits to room temperature before serving. Store in a sealed container for up to 3 days.