For the cake layer:

Preheat the oven to 350°F (175°C).

Line the bottom of an 8-inch (20 cm) round pan with parchment. Do not grease the sides.

Place the eggs and sugar in a mixing bowl. Beat on medium-high speed for about 5–7 minutes, until the mixture becomes pale, thick, and tripled in volume. When lifted, the batter should fall in ribbons that briefly sit on the surface. Beat in the vanilla.

In a separate bowl, whisk together the flour, cornstarch, and salt. 

Sift this mixture over the whipped eggs in two additions, gently folding with a spatula after each addition. 

Fold carefully to avoid deflating the batter.

Take a small scoop of batter and stir it into the melted butter to lighten it. Fold this mixture back into the main batter until just combined.

Pour into the prepared pan and gently level by tapping it on the counter.

Bake for 15–18 minutes, until the top springs back lightly and the cake pulls slightly from the edges.

Cool in the pan for 10 minutes, then run a knife or offset spatula around the edge and turn out onto a rack to cool completely.

When completely cooled, use a serrated knife to cut off the top if domed. Place the cake into the bottom of an 8” springform pan. Set aside.

For the cheesecake layer: 

Beat the mascarpone, cream cheese, sugar, and Baileys with an electric mixer or whisk until smooth. 

Spread the cheesecake mixture over the cake and chill for at least 2 hours. Overnight works best.

Remove the chilled cheesecake from the fridge. Let it sit at room temperature for 10 minutes, then unlatch the side piece and lift it off the cake. 

Use a large spatula to transfer the cake from the base of the springform pan to a cake stand or cake plate. Use an offset spatula to smooth the sides where the cake and cheesecake meet. Dip the spatula in hot water and wipe with a clean towel between smoothings. 

Refrigerate until ready to add the toppings. 

For the toppings and garnishes:

To make the St. Patrick’s Day pretzels, melt 2 ounces of white chocolate in the microwave in 30-second intervals. 

When fully melted, dip the top of the pretzel into the melted white chocolate. Allow the excess chocolate to drip back into the bowl. 

Then dip into the green nonpareils and lay flat to dry. Allow the chocolate to harden for a few minutes before adding it to your cheesecake.

Whip the cream, dollop it on top of the cake, and spread it around to within an inch of the edge.

Drizzle the caramel over the top of the cheesecake and down the sides.

Place the pretzels around the perimeter of the cake.

Drop popcorn or caramel corn on top, allowing it to catch on the pretzels and for some to go off the edge.

Keep refrigerated until serving time.