Whisk egg yolks in a medium-sized heat-proof bowl until smooth and starting to lighten in color.

Slowly ladle in 1/4 cup of warm milk mixture at a time, slowly drizzling the hot liquid into the yolks as you whisk vigorously. Repeat with a few more ladles full, whisking constantly, until the yolk mixture is noticeably warm to the touch (I usually do about half of the milk mixture just to be safe). Pour into saucepan with remaining milk mixture and return to heat.

Continue to cook over medium-low heat, stirring regularly, until mixture has thickened slightly and coats the back of the spoon; it should register approximately 170 to 175 degrees on an instant read thermometer. Remove from heat.

In a blender or food processor, blend banana with about 1/2 cup of warm milk mixture until smooth. Blend in guar gum (if using). Stir into saucepan with rest of warm milk mixture along with remaining 1/2 cup heavy cream and vanilla. Strain through a fine mesh sieve to remove any bits of cooked egg or larger bits of banana.

Transfer to a bowl or 4-cup glass measuring cup. Set inside a larger bowl, then fill the space between with ice water. Stir occasionally until mixture has cooled to lukewarm, then cover tightly (pressing a layer of plastic wrap onto the surface of the custard) and refrigerate for at least 2-3 hours or ideally overnight.

To make fudge chunks, combine chopped chocolate, cream and corn syrup in a small saucepan set over very low heat (I used our 'melt' burner for this, you can also use a double boiler if you have one). Gently warm the mixture until chocolate is melted and mixture forms a smooth, glossy paste about the consistency of peanut butter.

Transfer chocolate mixture to a piping bag fitted with a 1/4 or 3/8-inch round tip. Pipe ropes of chocolate onto a cookie sheet lined with parchment paper or a silicone mat. Alternatively, you can pour the chocolate out onto a lined cookie sheet and spread it into an even layer approximately 3/8-inch thick. Let cool for 30 to 60 minutes, then loosely cover and refrigerate for at least 1 hour until completely set, or freeze for 15 to 30 minutes. Once the chocolate is firm, cut into small pieces. Work quickly, as the chocolate will get melty again quite quickly (refreeze for a few minutes if needed). If you spread the chocolate instead of piped it, just cut a small grid of chocolate so you have approximately 3/8-inch bits. Return cut chocolate pieces to freezer until you're ready to use them.

Churn ice cream base in an ice cream maker according to manufacturers instructions. When the ice cream reaches the consistency of soft serve, add frozen chocolate chunks and stir until evenly incorporated. Transfer to a freezer storage container, ideally one with a lid (you can also press a layer of parchment or plastic wrap down on the surface of the ice cream) and freeze until firm, at least 3 hours or overnight.