Whisk together dry ingredients: in a medium bowl, sift or whisk 1.5 cups all-purpose flour, 1 cup granulated sugar, 1.5 tsp baking powder, and 1/2 tsp salt until evenly combined.

Cream the butter and some sugar: in a large bowl or the bowl of a stand mixer fitted with the paddle attachment, beat 1/2 cup softened unsalted butter on medium speed until smooth, about 30–45 seconds. Add half of the sugar mixture (about half of the dry mix) and beat briefly to incorporate. This step ensures butter is aerated.

Add egg whites and extracts: add the 3 large egg whites one at a time, beating on low speed after each addition until incorporated. Add 1 tsp vanilla extract and 1/4 tsp almond extract and mix briefly.

Alternate adding dry and wet: with the mixer on low, add the remaining dry ingredients in three additions alternating with the milk and sour cream: add one-third of the dry mix, then half of the milk (1/4 cup), then next third of dry, then remaining milk (1/4 cup) plus the 1/4 cup sour cream, then the final dry. Mix just until combined after each addition; do not overmix.

Scoop and bake: divide batter evenly among the 12 liners (about 2/3 full each). Bake in the preheated 350°F oven for 16–20 minutes, or until a toothpick inserted near the center comes out clean and tops are pale golden. Rotate the pan halfway through baking if your oven is uneven.

Cool completely: remove cupcakes from the oven and let cool in the pan for 5 minutes. Transfer to a wire rack to cool completely before frosting (at least 45 minutes).

Toasted Almonds & Finish

Toast the almonds (dry): while cupcakes bake or cool, spread 3/4 cup sliced almonds in an even layer on a baking sheet. Toast in the oven at 350°F for 6–8 minutes, stirring once, until fragrant and just golden. Watch closely so they don't burn. Alternatively, toast in a dry skillet over medium heat for 4–6 minutes, stirring frequently.

Optional Caramelized Almonds

For a sweet crunchy finish: in a small skillet over medium heat melt 1/2 tbsp butter, add 1 tbsp granulated sugar and let it dissolve and begin to bubble. Add the toasted almonds and stir to coat; cook 1–2 minutes until sugar crystallizes or lightly caramelizes. Transfer to parchment to cool and separate. Use cooled almonds for decoration.

Prepare garnish: once cooled, roughly chop any larger caramelized almonds if desired or keep sliced toasted almonds whole for sprinkling.

Amaretto Buttercream

Beat the butter: in a large bowl or stand mixer fitted with the paddle attachment, beat 1 cup (2 sticks) softened unsalted butter on medium-high speed for 1–2 minutes until creamy and pale.

Add sugar gradually: reduce speed to low and add 3.5 cups sifted confectioners' sugar in two or three additions, scraping the bowl between additions. Once incorporated, increase speed to medium and beat 30 seconds to aerate.

Flavor and thin: add 2 tbsp amaretto liqueur, 1 tsp vanilla extract, 2 tbsp heavy cream, and 1/8 tsp fine salt. Beat on medium-high for 1–2 minutes until light, smooth, and spreadable. If the frosting is too stiff, add additional 1 tsp increments of cream; if too thin, add up to 1/2 cup more powdered sugar to reach desired piping consistency.

Taste and adjust: taste a small amount and, if you want a stronger almond note without more alcohol, add up to an additional 1/4 tsp almond extract (optional) and beat briefly to incorporate.

Pipe or spread: transfer buttercream to a piping bag fitted with a large round or star tip (or use a spatula). When cupcakes are completely cool, pipe a generous swirl of amaretto buttercream onto each cupcake.

Finish with almonds: immediately after piping, press a few toasted or caramelized almond slices into the frosting and optionally sprinkle a pinch of sanding sugar for sparkle.