Preheat oven to 350°F (175°C), line cupcake pans with liners.
Whisk flour, sugar, baking powder, and salt in a bowl.
Beat butter in a large mixing bowl until creamy, gradually add sugar and mix until light and fluffy.
Add eggs one at a time, mixing well after each addition.
Alternately add flour mixture and milk, mixing on low until just combined.
Stir in vanilla and pecans (optional).
Divide batter into prepared pans, fill 2/3 full.
Bake 18-20 minutes until a toothpick inserted comes out clean.
Cool completely before frosting.
For frosting, beat butter until smooth, gradually add confectioners’ sugar, 1 cup at a time.
Add 1 teaspoon vanilla and beat until light and fluffy, adjusting with 1-2 tablespoons milk if needed.
Divide frosting into two bowls: tint one with red beet juice for cap color.
Spoon cake batter into bowls, halved vertically, and fill with 1 tablespoon plain buttercream.
Frost tops of cupcakes with plain frosting, using a small offset spatula for a smooth base.
Dip small paintbrush into red frosting and dab 3-4 stripes at the bottom of each cupcake to form the mortarboard lines.
Using a small piping tip, pipe a white doughnut ring around the cupcake’s edge just above the red stripes.
Press 3-4 almond slivers into the ring to create a banner shape for the graduation cap.
Use a paintbrush to dab a red-tinted frosting stripe along the center of the cap, curve it into a “V” shape at the bottom for a diploma look.