Preheat Oven & Prepare Muffin Pan: Preheat the oven to 356ºF (180ºC) fan-forced. Grease a 6-hole muffin pan with butter and dust with flour to ensure smooth cake sides. Set aside.
Mix Dry Ingredients: In a medium-sized mixing bowl, whisk together flour, baking powder, and salt. Set aside.
Cream: In a separate large mixing bowl, using either electric hand beaters or a stand mixer with the paddle attached, add softened butter, sugar and vanilla extract to the bowl. Beat for 2 minutes until pale and creamy, scraping down the sides as needed.
Add Egg: Add the egg and beat for 15 seconds, scrape down the sides.
Add Liquids: Pour in milk and oil, beating for 20 seconds until well combined.
Combine with Dry Ingredients: Add the flour mixture and beat until incorporated. Ensure not to over-beat, about 10-15 seconds. If excess flour is visible, gently fold it in with a rubber spatula.
Fold in Raspberries: Add the raspberries and gently fold them through the batter just until distributed. Do not over-mix.
Distribute Batter: Spoon the batter evenly into the prepared muffin pan. The batter will reach the top of each muffin hole.
Bake: Bake for 20-22 minutes, or until a skewer inserted into one of centers comes out with a few moist crumbs, not wet batter. It's okay if the skewer has some wet raspberries on it, as this just indicates the juiciness of the fruit, not undercooked batter.
Cool: Allow the cakes to cool in the pan for 10 minutes, then carefully remove and transfer them to a wire rack to cool completely.
To Serve: Dust with powdered sugar to serve. Enjoy!