Preheat the oven to 350°F (175°C). Lightly grease a 9 × 13-inch baking pan.
Spread the crushed strawberries evenly over the bottom of the prepared pan.
Sprinkle the dry strawberry gelatin evenly over the fruit, then add the miniature marshmallows in an even layer.
Prepare the yellow cake batter according to the package directions. Pour it carefully over the marshmallows and spread it to the edges.
Bake for 40–50 minutes, until a toothpick inserted in the cake layer comes out clean.
Cool in the pan for 15 minutes. Run a thin knife around the edges to loosen the cake.
Place a large serving tray over the pan and carefully invert the cake. Refrigerate leftovers.