Preheat oven to 400°. Put cherries and 3 tbsp. of the sugar into a medium saucepan. Heat over medium-low heat, gently stirring occasionally, until sugar dissolves and cherries are warmed through, 8–10 minutes.
Meanwhile, combine flour, baking powder, and 3⁄4 cup of the sugar in a medium bowl. Stir in egg with a fork, then use your fingers to work in egg until topping is crumbly. Set aside.
Put cherry mixture into an 8" x 8" baking dish, then scatter topping over it in an even layer. Drizzle melted butter over topping and sprinkle the remaining 1 tbsp. sugar on top. Bake until topping is golden brown, 15-20 minutes. Set aside on a rack to cool briefly before serving or serve at room temperature.