Preheat the oven to 350°F (180°C). Prepare a 12-cup muffin pan with paper liners. Set aside.
In a small bowl combine flour, baking powder, and salt. Set aside.
In the bowl of a stand mixer fitted with the paddle attachment, beat the butter and sugar together on medium-high speed until light and fluffy, about 2-3 minutes.
Add lemon zest and eggs. Beat on medium-high speed until everything is combined, about 2 minutes.
Add the flour mixture to the wet ingredients in three additions, beating on low speed after each addition.
Beat in the milk and lemon juice on low speed until just combined. Do not overmix the batter!
Half-fill each liner with the batter and make a small well in the center. Fill the well with a teaspoonful of the lemon curd (my easy lemon curd recipe) and cover with more of the cupcake mixture so the liners are three-quarters full.
Bake for 18-20 minutes. A toothpick inserted in the middle will come out clean when done. Remove from the oven and allow to cool completely before frosting.
While waiting for the cupcakes to cool make the raspberry puree for the frosting. In a small saucepan bring frozen raspberries to a simmer over medium heat.
Stir the mixture occasionally, breaking up the berries, until the raspberries have become soft enough to mash and look like raspberry jam. Let simmer until the mixture can coat a spoon, then remove from heat.
Strain the mixture through a sieve, discard the seeds. Allow mixture to cool completely before using. This should make 1/4 cup raspberry puree without seeds.
In the heatproof bowl of a stand mixer set over a saucepan of simmering water, combine the sugar and egg whites. Cook, whisking constantly until the sugar has dissolved and the mixture is warm to the touch.
Attach the bowl to a stand mixer fitted with the whisk attachment. Beat the mixture on high speed until it holds stiff peaks and the mixture is fluffy and completely cooled, about 6 minutes.
Switch to the paddle attachment. Add several tablespoons butter at a time with the mixer running on medium-low speed. Beat well after each addition!
Beat in vanilla extract. Switch to the lowest speed to eliminate air bubbles, about 2 minutes. Using a rubber spatula, stir in 1/4 cup of the cooled raspberry mixture until frosting is smooth.
Frost cooled cupcakes as desired. To make roses use a Wilton 1M tip. Start in the center, then slowly move your tip in a circle around the center point.