1. Preheat the oven to 375ºF. Make filling: Melt 3 Tbsp. butter in a 10 1/2-inch cast-iron skillet over medium-high heat. Add peaches and cook, stirring occasionally, until they begin to soften, 3 to 4 minutes. Add 1/4 cup sugar, cinnamon and a pinch of salt and cook, stirring frequently, until sugar has dissolved and peaches are soft and most of their liquid has evaporated, 3 to 5 minutes longer. Remove skillet from heat.
2. Combine flour, baking powder, 1/2 tsp. salt, remaining 1/2 cup sugar and remaining 13 Tbsp. butter in a food processor; pulse until mixture resembles coarse meal. With motor running, add milk and vanilla, and process just until a rough dough forms.
3. Drop spoonfuls of topping over warm peaches and sprinkle with almonds, if desired. Bake until topping is golden, 30 to 35 minutes. Let stand 15 minutes. Serve warm, topped with a scoop of vanilla ice cream, if desired.