Prep the oven and pan. Heat oven to 350°F (175°C). Line a 12-cup muffin tin with paper liners.

Mix dry ingredients. In a bowl, whisk flour, sugar, baking powder, baking soda, and salt.

Mix wet ingredients. In another bowl, whisk melted butter, eggs, vanilla, milk, and yogurt until smooth.

Combine batter. Add wet to dry and stir just until no dry streaks remain. Don’t overmix.

Fill and bake. Divide batter among liners (about 2/3 full). Bake 16–20 minutes, until a toothpick comes out clean. Cool completely on a rack.

Make buttercream. Beat butter until creamy. Add powdered sugar, salt, vanilla, and 1 tbsp milk. Beat until fluffy, adding more milk if needed. You want a medium-thick consistency.

Pipe the “stems.” Transfer buttercream to a piping bag fitted with a round tip (or snip a corner of a zip-top bag). Pipe a tall mound in the center of each cupcake—about 1 to 1.5 inches high. Smooth the sides lightly; this becomes the mushroom stem.

Make the red cap coating. Melt white chocolate with oil in short microwave bursts or over a double boiler. If using white chocolate, tint with red gel food coloring until vivid red. If using red candy melts, just melt and thin with a little oil for smooth dipping.

Attach the caps. Spoon a generous dome of red coating over each buttercream mound, letting it gently drip to form a rounded cap. Or chill the cupcakes 5–10 minutes, then dip the buttercream mounds straight into the red coating for an even finish. Let set 10–15 minutes.

Add white spots. Use melted white chocolate in a small bag (snip a tiny tip) to dot small and medium circles over the red caps. You can also press on white sprinkles before the red sets. Aim for a random pattern to look natural.

Finish and serve. Chill for 10 minutes to firm up, then bring to room temperature before serving so the frosting is soft and the caps are set.