Lemon and Raspberry Cupcakes

Raspberry Jam Cake Filling
29 Place raspberries, sugar, and lemon juice in a medium saucepan over medium heat for 10-12 minutes until boiling, mash with a wooden spoon to help break down the berries.  
30 Whisk together the cornstarch and water in a small bowl, then stir into the jam.  Cook for an additional 1-2 minutes until thickened. 
31 *Option to press jam through a metal mesh sieve while its still warm to remove the seeds. 
32 Transfer jam to a heat proof container or bowl to cool completely before assembling cupcakes. Jam can also be made ahead and stored in air tight container.
Cupcake Batter
2 Preheat Oven to 350℉ / 180℃ / 160℃ Fan (convection). Line a 12-cavity cupcake pan or 6 cavity large muffin pan with paper cupcake liners.
3 In a medium bowl, hand whisk together flour, salt, and baking agents. Set aside.
4 Place the sugar and lemon zest into the bowl of a stand mixer. Work the zest into the sugar by rubbing it together with your fingertips. Add in the flour mixture and mix together on low speed with the paddle attachment to distribute. 
5 Add in the softened butter and mix until just combined.(about 1 minute). It should look like a shaggy corneal texture. 
26 In a small bowl whisk together the eggs and vanilla. Pour the egg mixture into the batter and beat on medium high for 2-3  minutes until light and fluffy. Scrape the bottom and sides of your bowl to catch any ingredients that are just hanging around. 
6 Lastly, pour in the lemon juice and buttermilk slowly until the cake batter is smooth and fluffy. Scrape the sides and bottom of the bowl one last time to make sure everything is mixed in.
7 Divide the cupcake batter into the paper liners of your pan. Fill them 3/4 of the way full to create a small dome when baked. I use a large ice cream scoop to make measuring easier. 
9 Bake 12-cavity regular cupcakes for 15-18 minutes or the 8-cavity jumbo cupcakes for 20-25 minutes until lightly golden or when a toothpick  inserted into the center comes out clean. Repeat with remaining batter.
10 Place cupcake pan on wire cooling rack to cool 10 minutes. Remove each cupcake and place on rack to cool completely before decorating.
Fill the Cupcakes
23 Take a small knife and cut a circle out of the center top of each cupcake. Removing about a teaspoon or two of cake crumbs with a lemon baller or teaspoon. Fill the holes with raspberry jam. 
Raspberry Swiss Meringue Buttercream
14 Clean and dry your stand mixer bowl and whisk attachment. Wipe down lightly with lemon juice to remove any residue.
15 Add the egg whites and sugar to the bowl of a stand mixer. Create a double boiler by placing the bowl over a pot of shallow simmering water. Do not let the mixing bowl touch the water.
16 Whisk the egg whites and sugar continuously until the temperature on an instant thermometer reads 160℉ (72℃). Carefully dip your finger into the hot sugar and rub the mixture between your fingertips. If you don't feel any grains of sugar, the mixture is ready. (about 6-8 minutes)
17 Remove the mixing bowl from the heat and wipe the bottom of the bowl dry with a towel. Place the bowl on the mixing stand fitted with the whisk attachment and begin whipping on medium-high speed.
18 Continue to whip until a thick, glossy and marshmallow like meringue with stiff peaks is formed. The bowl should no longer be warm or at least room temperature to the touch. Its ok if the very bottom of the bowl is slightly warmer than room temperature. (about 10-15 minutes)
20 Switch to the paddle attachment on the mixer. (You can continue with the whisk attachment if you prefer and switch to the paddle attachment at the end to beat out any air bubbles.)
21 While mixing on medium speed drop in one tablespoon of butter at a time into the whipping meringue. Wait for each piece of butter to mix-in before adding the next. 
33 You may notice the meringue losing its stiffness and becoming softer, that's ok, keep adding butter.
34 Once half of the butter has been mixed in, stop the mixer and scrape the bottom and sides of the bowl to grab any stuck meringue or bits of butter. We want all the butter to emulsify with the meringue.
35 Continue mixing and add in the remaining butter.
36 The meringue may deflate and look runny or split, but keep mixing for another 10-15 minutes after all the butter has been added on medium speed.
37 If after 10 minutes of mixing it hasn't magically transformed into a frosting texture, just place the bowl in the fridge for 10 minutes with the paddle attachment. Then, whip again until silky smooth.
38 Once the buttercream looks like a spreadable frosting add in the vanilla bean paste and salt, then give it a couple spins on low to mix.
39 Add in the raspberry jam and mix in on low speed.
42 If you would like your frosting to have more color, mix in a couple drops of gel food color.
40 If there are a bunch of air bubbles in the frosting, mix on low speed with the paddle attachment until smoother.
41 Transfer buttercream to a large piping bag with desired piping tip. Pipe starting on the outer edges, working your way into the middle of each cupcake in a circular motion. Lift up once you reach the center. Repeat with remaining cupcakes.