Melt the butter in a skillet until browned (not burned!), with a warm nutty aroma. You can find a fantastic tutorial on browning butter over at Simply Recipes. Strain and set aside to cool.
Make your crumble: Rub flour and butter together with your fingers, or with a pastry cutter, until it forms coarse crumbs. Mix in the sugar and nuts. Set aside in the refrigerator until ready to use.
Butter a 8-inch cake pan and lay your pear cubes at the bottom of the pan.
Mix the sugar with the egg. Whisk your flour and baking powder together, then add to the egg mixture. Add the (cooled) brown butter. Pour the batter over the pears.
Get your crumble mixture and sprinkle over the top of the batter until fully covered. You may not use it all**.
Bake in a 180C (350F) oven for 40-50 minutes or until a pick inserted in the middle of the cake comes out clean.
Let the cake rest in its pan for about 5-10 minutes. Turn out into a plate, and then turn over onto another plate so the pears are on the bottom and the crumble on top.