Preheat oven and prep pan:

Set oven to 350°F (175°C) with a rack in the middle. Fit a 12-cup muffin pan with paper liners.

Mix cupcake batter:

In a mixing bowl, whisk together self-rising flour, baking powder, granulated sugar, 1/2 cup softened butter, eggs, and 1 tsp vanilla. Using an electric mixer on medium, beat for roughly 2 minutes until the mixture turns pale and smooth; avoid overbeating.

Bake and cool cupcakes:

Portion the batter into the liners, filling each to about two-thirds full. Bake for 20-25 minutes, until golden and the tops bounce back when lightly pressed; refrain from opening the oven before 15 minutes have passed. Let cool in the pan for 5 minutes, then move to a wire rack to cool fully.

Make buttercream frosting:

For the buttercream: In a separate bowl, cream 6 tbsp softened butter until smooth. Slowly incorporate the sifted powdered sugar, then mix in 1/2 tsp vanilla and milk until the buttercream is light and easy to spread.

Frost and fill cupcakes:

Frost each cooled cupcake with buttercream. Create a small well in the center and add a generous spoonful of raspberry jam.