FOR PRETZEL CRUST:
1. Using a food processor, pulse pretzels until they are a fine crumb consistency.

2. Add brown sugar and salt, pulse to combine.

3. Add melted butter and pulse until completely combined and crumbs are saturated, scraping down the sides of the bowl when needed. Set aside.

FOR BLUEBERRY PUREE:
1. In a food processor, add blueberries and water. Puree.

2. In a small saucepan, add blueberry puree, sugar, lemon juice, and blueberry flavor fountain.

3. Simmer over low heat until the mixture thickens, approximately 15 minutes.

4. Transfer to heat-safe bowl and set aside.

FOR SEMIFREDDO:
1. To the bowl of a stand mixer, add heavy cream and blueberry flavor fountain.

2. Using the whisk attachment, whip to soft peaks. Cover and refrigerate.

3. Whisk sugar and eggs in double boiler until mixture has doubled in volume, is pale, and is warm to the touch. Approximately 4 minutes.

4. Remove from heat and whisk for an additional minute.

5. Fold in whipped cream, making sure no streaks remain.

ASSEMBLY:
1. Line the bottom of a 9-inch springform pan with parchment paper, and the sides of the pan with an acetate collar.

2. Add pretzel crust mixture, firmly pressing across the bottom to create an even layer.

3. Pour half of the semifreddo mixture into the springform pan. Tap the pan to help spread.

4. Drizzle half of the blueberry puree on top and use a knife or skewer to swirl into the semifreddo.

5. Add the remaining semifreddo, drizzle with the blueberry puree, and repeat the swirling technique.

6. Freeze for at least 8 hours.

7. When ready to serve, remove side of pan and acetate collar. Using a warm knife, cut clean slices and garnish with lemon curd, mint leaves, and fresh blueberries (optional).