Preheat your oven to 375°F / 190°C. To make the glaze, melt 4 tablespoons (60 ml / 2 fl oz) of butter in a small saucepan over low heat.
Brush the bottom and sides of a 9x9-inch square cake pan with some of the melted butter.
Add the dark brown sugar to the remaining butter in the saucepan and stir until fully melted and combined.
Pour this caramel mixture into the prepared cake pan and spread it evenly across the bottom. 2.
Arrange the sliced pears over the caramel in a neat, decorative pattern. You can create tight rows or a fanned-out design. If you have any leftover pear slices, chop them finely and scatter them over the first layer to fill any gaps. 3.
In a large bowl, use an electric mixer to cream the 4 tablespoons (60 ml / 2 fl oz) of softened butter, granulated sugar, and vanilla extract until the mixture is light and fluffy.
Add the egg and beat again until it's fully incorporated and the mixture is creamy. 4.
In a separate medium bowl, whisk together the flour, cinnamon, baking powder, and salt.
Add about a third of this dry mixture to the wet , beating on low speed until just combined.
Pour in half of the milk and mix again.
Repeat, alternating between the dry and wet and ending with the dry mixture. Be careful not to overmix. 5. Gently pour the cake batter over the layer of pears in the pan. Use a spatula to spread the batter evenly, making sure it reaches all the corners. 6.
Bake for 30 to 35 minutes, or until a wooden skewer or knife inserted into the center of the cake comes out clean. 7.
Let the cake cool on a wire rack for 10 minutes. This is crucial—if it's too hot, it will fall apart; if it's too cool, the caramel will stick. Run a knife around the edges of the pan to loosen the cake.
Place a large serving platter over the top of the cake pan and, using oven mitts, carefully and quickly flip it over. Lift the pan away to reveal the pear topping.
Serve warm or at room temperature, with a dollop of whipped cream or a scoop of vanilla ice cream if desired.