Whisk together the melted butter, sugar and salt. Add flour and ground almonds and stir until it feels like damp sand. Press dough evenly along bottom and halfway up the sides of an 8-inch round tart pan with a removable bottom. Use waxed paper or buttered fingers to even out and press dough tightly into the corners. Prick crust all over with a fork and chill while you preheat oven to 350 degrees about 30 minutes. Set pan on a baking sheet and bake until crust is golden brown, about 25 minutes.
While crust bakes, bring milk, agave and salt to a simmer in a medium saucepan over low heat. Remove from heat and pour over chocolate in a medium heatproof bowl. Let it sit for about 2 minutes without stirring. Starting in the middle of bowl, whisk chocolate together until evenly melted and the mixture a smooth and shiny dark brown.
Fan pear slices around bottom of the tart shell in one even layer. Whisk beaten egg into the chocolate filling and pour filling over pears and crust. Decrease oven temperature to 300 degrees and return tart to oven; bake until filling is set but still a little wiggly in the center third, about 15 minutes. Remove and cool tart completely on a rack at room temperature. Remove tart from pan sides and carefully transfer to a platter. Slice and serve slightly warm or at room temperature.