Preheat the oven to 350°F (175°C).
In a mixing bowl, combine flour, sugar, baking powder, and salt. Mix until well combined.
In another bowl, cream together the softened butter, milk, egg, and vanilla extract until smooth.
Gradually mix the dry ingredients into the wet mixture until combined, being careful not to overmix.
Pour the batter into a greased 9-inch round baking pan.
Bake in the preheated oven for 20-25 minutes, or until a toothpick inserted into the center comes out clean. Let it cool completely.
While the cake is cooling, prepare the strawberries. Toss the sliced strawberries with 2 tablespoons of sugar and set aside to macerate for about 10 minutes.
In a mixing bowl, whip the heavy cream, powdered sugar, and vanilla extract until soft peaks form.
Once the cake is cooled, cut it into small cubes.
To assemble, layer the ingredients in jars: start with a layer of cake cubes, followed by a layer of macerated strawberries, and then a layer of whipped cream. Repeat until the jars are filled, finishing with whipped cream on top.
Chill the dessert in the refrigerator for at least 30 minutes before serving for the best flavor.