Heat oven to 325 degree F. Grease and flour giant cupcake pan (find it here: familycircle.com/pan) and set aside.

Cake: Whisk together flour, poppy seeds, baking soda and salt in a medium bowl. Set aside.

Beat butter and cream cheese with an electric mixer in a large bowl until smooth. Add granulated sugar and beat on medium until light and fluffy, about 3 minutes. Add eggs, one at a time, beating well after each until well combined.

Combine the buttermilk, lemon juice and zest in a liquid measuring cup. Add the flour mixture, alternating with the buttermilk mixture, to the butter mixture, starting and ending with the dry ingredients. Beat until just blended.

Divide batter evenly between prepared pan halves. Bake until a toothpick inserted in centers comes out clean, about 1 hour. Transfer to a wire rack and cool 10 minutes. Invert; cool completely.

Trim cakes if necessary. Place bottom part of the cupcake on a wire rack over a jelly roll pan, top-side down.

Make Glaze: In a medium-size bowl, whisk together the confectioners' sugar, lemon juice and food coloring until smooth. Pour glaze over the bottom half of cake to cover completely; use a spatula to help spread it onto side of cake. Let dry 5 minutes, then repeat, scraping up glaze from the pan and reusing excess. Let stand until glaze is set, about 15 minutes.

Meanwhile, make Frosting: In a large bowl, beat together butter and cream cheese. Add the confectioners' sugar and lemon juice and beat on low speed until smooth and good spreading consistency.

Turn over cupcake bottom and spread with a little frosting. Attach top of cupcake (trimmed level if needed) and spread with remaining frosting. Decorate with berries and sprinkles and add candles or sparklers, if desired.