• ½ cup (1 stick) unsalted butter, at room temperature, plus more for the pan
• 2 cups sifted all-purpose flour
• 1 teaspoon baking powder
• ⅛ teaspoon salt
• 1 cup granulated sugar
• 1 large egg
• 1 teaspoon pure vanilla extract
• 1 (13- to 14-ounce) loaf guava paste, cut into ¼-inch-thick slices
• 1 tablespoon powdered sugar

Preheat the oven to 350°F. Butter and lightly flour a 9- to 10-inch round or square false-bottomed tart or cake pan.

Sift together the flour, baking powder, and salt. With an electric mixer, cream the butter and granulated sugar and mix in the egg. Gradually beat in the flour mixture, alternating with 1 tablespoon cold water and the vanilla, to form a stiff dough. Gather the dough into a mass; divide it in half and form it into 2 balls. If not using immediately, wrap each ball tightly in plastic wrap and refrigerate.

On a lightly floured surface, roll one of the dough balls into a circle or square large enough to line the prepared pan. Carefully roll the dough up on the rolling pin and unroll it into the pan, pressing it gently into the bottom and against the sides. Cover the bottom of the tart with the guava slices.

Roll out the remaining dough ball into a round or square about ¼ inch thick and large enough to cover the top of the tart. For a plain top crust, roll the dough up on a rolling pin and unroll it on top of the guava. Trim the edges with kitchen scissors or a sharp knife.

For a more decorative top crust, use a 3- to 4-inch heart-shaped cookie cutter to cut out shapes. Arrange the pastry cutouts on top of the guava, with their sides touching and points toward the center.

Bake the tart on the middle rack of the oven for 30 to 40 minutes, or until the crust is golden brown. Let the tart cool in the pan, on a rack, for 10 minutes. If necessary, gently insert the point of a small, sharp knife between the top edge of the tart and the pan to loosen it. Carefully place the tart on top of a 1-pound can. The sides of the pan should slip down. Let the tart finish cooling on the rack. Do not remove the bottom of the pan. Just before serving, sprinkle lightly with powdered sugar. Cut into wedges or squares and serve.