For the sponge: Firstly preheat the oven to 180C/160C Fan/Gas Mark 4, and line one or two large cupcake/muffin tin(s) with 8 cupcake/muffin cases. Then set aside.
Place the butter into a large bowl and beat with an electric hand-whisk until light and fluffy. Then beat in the sugar until well combined and fluffy. Then add the vanilla, and the eggs one at a time - beating well between each addition.
In a small bowl, combine the flour, baking powder and salt. Then beat into the wet batter in three additions, mixing until just combined each time. Finally, beat in the milk until just combined and divide the batter between the cupcake/muffin cases. Bake for 23 minutes, until the cupcakes are a golden brown and springy to the touch. Place the cupcakes onto a cooling rack and leave to cool completely.
For the filling: In a small bowl, mix the jam to loosen a little. Then using either an apple corer or small paring knife, core the cupcakes and fill each with the jam to the brim.
For the topping: Pour the cold cream into a large bowl and using an electric hand-whisk, whisk on a high speed until stiff peaks. Then spoon into a piping bag fitted with a star tip (I used Wilton 2D). Pipe swirls over each cupcake. Finally, slice the strawberries in half and place one into the top of each cupcake.