Preparation

• Heat the oven to 350°F and lightly butter the sides of an 8-inch square pan.

Make the caramel:

• In a small saucepan, combine the brown sugar and butter. Cook over medium heat, stirring often, until the butter is melted and the mixture is smooth. Bring to a boil and pour into the prepared pan. Spread with a spatula to coat the bottom evenly. Scatter or arrange the pineapple slices evenly in the caramel, overlapping them slightly. Gently press the fruit into the caramel.

Make the cake:

• Sift together the cake flour, baking powder, and salt. In a medium bowl, beat the butter with an electric mixer until smooth. Gradually add the sugar and continue beating until fluffy and lighter in color, about 3 min. Beat in the orange zest and vanilla. Add the eggs one at a time, beating briefly after each addition. Sprinkle half of the flour mixture over the butter mixture and, on low speed, mix just until the flour disappears. Add the yogurt and mix until just blended. Gently mix in the remaining flour. Scoop large spoonfuls of batter onto the fruit; gently spread the batter evenly in the pan. Lightly tap the pan on the counter to settle the batter. Bake until the cake is golden brown and a pick inserted in the center comes out clean, about 45 min. Immediately run a paring knife around the inside edge of the pan. Set a flat serving plate on top of the pan and invert the cake. Let the inverted pan rest for about 5 min. to let the topping settle. Gently remove the pan and serve the cake warm or at room temperature.