Start by gathering all your ingredients on the countertop. Make sure your butter is at room temperature. Preheat your oven to 350°F (175°C).
In a large mixing bowl, whisk together the all-purpose flour, baking powder, and a pinch of salt to aerate and mix evenly.
In another bowl, cream the room-temperature salted butter with the brown sugar until light and fluffy, about 3-4 minutes on medium speed using an electric mixer.
Add the milk and vanilla or almond extract to the butter-sugar mixture and mix until well combined, even if it looks slightly curdled.
Gradually add the dry ingredients to the wet mixture, mixing until just combined. Avoid over-mixing to keep biscuits tender.
Turn the dough out onto a lightly floured surface and gently knead a few times until it comes together. Roll the dough to about 1/4 inch thick.
Cut out shapes using cookie cutters or knife. Place half the shapes on a parchment-lined baking sheet. Place a small piece of guava paste in the center of each biscuit, then top with another biscuit shape, sealing edges gently.
Bake the biscuits for 12-15 minutes, or until lightly golden around the edges.
Remove biscuits from oven and let cool slightly. While still warm, roll each biscuit in powdered sugar until fully coated.