Pour the heavy cream into in to a small saucepan set over medium-high heat. Heat until small bubbles start to form around the edge of the pan. Place the chocolate chips, hazelnut spread, espresso and salt in a medium bowl. Pour the hot cream over the chocolate and let stand for 1 minute to soften. Starting in the center of the bowl, whisk the chocolate mixture in small circles until smooth and combined. Cool to room temperature.
Cover with plastic wrap and refrigerate for 2 hours.
Using an electric hand mixer on medium speed, beat the chocolate mixture until light, slightly thickened and spreadable, 5 minutes.
Place the bottom half of the cake on a cake plate. Spread one-quarter of the frosting on top of the cake, leaving a 1/4-inch edge. Place the top half of the cake on the frosting, smooth-side up and gently press down to seal the cake halves. Use a rubber spatula to spoon the rest of the frosting on top of the cake. Using a small offset spatula, push the extra frosting over the sides and the top. Smooth the sides until completely covered. Smooth the top of the cake or make a decorative pattern. Store the cake in the refrigerator until ready to serve. Bring the cake to room temperature for 15 minutes before serving. Garnish with colorful edible flowers to serve.