In a microwave-safe mug (at least 12 ounces), whisk together the flour, sugar, cocoa powder, baking powder, and salt with a fork until no lumps remain.
Add the egg, milk, oil, and vanilla extract to the dry ingredients. Stir gently with a fork just until combined and smooth, about 15-20 strokes. Don't overmix.
Pit and quarter the fresh cherries, then gently fold them into the batter along with the chocolate chips, distributing them evenly throughout.
Microwave on high power for 60-90 seconds, depending on your microwave wattage. The cake is done when the top looks just set and springs back slightly when touched. Start with 60 seconds and add 10-second intervals if needed.
Let the mug cake cool for 60 seconds before eating to allow the texture to set properly. Top with whipped cream, ice cream, or enjoy as is while still warm.