Preheat the oven to 180°C (350°F), Gas Mark 4. Grease a 23 cm (9-inch) round springform tin.
Place the torn sage leaves in a medium heatproof bowl. In a small saucepan, melt the 225 g butter over medium heat. Let it foam, turn amber, and develop a nutty aroma. Pour the hot brown butter over the sage — it will sizzle — and set aside to let the flavor infuse.
Wipe out the same saucepan. Add the 50 g butter and 100 g brown sugar and heat gently until the sugar dissolves. Cook for 2 minutes, stirring often. Pour the caramel into the prepared tin and spread it evenly. Arrange the pear slices on top, cut-side down. Add extra sage leaves if you like.
Remove and discard the sage from the cooled brown butter. In a large bowl, whisk together the brown butter, caster sugar, and eggs for 1–2 minutes until fully combined. Add the flour, ground almonds, baking powder, salt, and cinnamon. Fold gently with a spatula until the batter is smooth and evenly mixed.
Carefully pour the batter over the arranged pears. Bake for 50–55 minutes, or until a skewer inserted into the center comes out with a few moist crumbs. Cool in the tin for 10 minutes, then loosen the edges and invert onto a serving plate.
