In a saucepan on the griddle over high heat, combine sliced strawberries, a splash of water, sugar, and vanilla. Cook, stirring occasionally, until the mixture reduces and thickens to your desired consistency. Remove from heat and set aside.
Prepare the cornbread mix according to the package directions, using milk, oil, and the egg.
Lightly butter the griddle surface and allow it to heat to low–medium.
Pour portions of batter onto the griddle to form about six Johnny cakes.
Cook until the bottoms are set and lightly golden, then carefully flip (they are more delicate than traditional pancakes). Cook until fully done.