Heat the oven to 350°F (175°C). Generously butter a 9-inch round baking dish or an 8-inch square baking dish.
Place the pitted cherries in the prepared dish and sprinkle them with 2 tablespoons (25 g) of the granulated sugar. Toss gently to coat and spread the cherries into an even layer.
In a large bowl, whisk the eggs and remaining 6 tablespoons (75 g) granulated sugar until smooth and slightly lighter in color. Whisk in the milk, heavy cream, vanilla extract, and almond extract.
Add the almond flour, cornstarch, and salt. Whisk until the batter is smooth, with no visible pockets of almond flour. Stir in the softened tablespoon of butter.
Pour the batter evenly over the cherries. Scatter the sliced almonds over the top, if using.
Bake until puffed around the edges, golden on top, and set around the perimeter with only a slight wobble in the center, 35 to 40 minutes. A thermometer inserted into the custard should read at least 160°F (71°C).
Let the clafoutis stand for 10 to 15 minutes before serving. It will settle slightly as it cools. Dust with confectioners' sugar just before serving, if desired.