French Onion Soup Ice Cream with Caramelized Onion Swirl

**Caramelize the Onions:** Melt butter in a large skillet over medium-low heat. Add sliced onions and cook, stirring occasionally, until they are very soft, deeply golden brown, and caramelized (about 30-40 minutes). Be patient and avoid browning them too quickly, or they will become bitter. Add brown sugar and balsamic vinegar during the last 5 minutes of cooking. Stir in the chopped thyme. Remove from heat and let cool completely. If desired, use a food processor to coarsely chop the caramelized onions to achieve a more consistent swirl.

**Infuse Cream:** In a saucepan, heat heavy cream and milk over medium heat with a few sprigs of fresh thyme until just simmering. Remove from heat, cover, and let steep for 30 minutes. This will infuse the cream with a subtle thyme flavor.

**Make the Custard Base:** Remove thyme sprigs from the cream mixture. In a separate bowl, whisk together granulated sugar and egg yolks until pale and slightly thickened. Slowly pour the warm cream mixture into the egg yolk mixture, whisking constantly to prevent the eggs from scrambling. This process is called tempering.

**Cook the Custard:** Pour the custard mixture back into the saucepan and cook over medium-low heat, stirring constantly with a spatula, until the custard thickens enough to coat the back of the spatula (about 5-8 minutes). Do not let it boil. The custard is ready when you can draw a line through the coating on the back of the spatula with your finger and the line remains. If using a thermometer, the temperature should be around 170-175°F (77-79°C).

**Chill the Base:** Immediately pour the custard base through a fine-mesh sieve into a clean bowl to remove any cooked egg bits. Stir in vanilla extract and salt. Cover the bowl with plastic wrap, pressing it directly onto the surface of the custard to prevent a skin from forming. Refrigerate for at least 4 hours, or preferably overnight, until completely chilled.

**Churn the Ice Cream:** Pour the chilled ice cream base into your ice cream maker and churn according to the manufacturer's instructions (usually about 20-25 minutes).

**Swirl in the Caramelized Onions:** While the ice cream is still soft, transfer about 1/3 of it to a freezer-safe container. Spoon a layer of caramelized onions over the ice cream. Repeat layering with the remaining ice cream and caramelized onions, creating a swirl effect. Use a knife or skewer to gently swirl the onions into the ice cream.

**Freeze:** Cover the container tightly and freeze for at least 4 hours, or preferably overnight, to allow the ice cream to harden completely.

**Serve:** Let the ice cream soften slightly at room temperature for 5-10 minutes before serving. Enjoy this unexpected and delicious dessert!