For the Brown Butter Graham Cracker Crumble:
Preheat oven to 350.
Combine the crushed graham crackers and sugar in a bowl. Add the browned butter and use a fork to combine well. Spread in even layer on parchment lined baking sheet and bake for about 12-15 minutes, tossing occasionally until very lightly brown. Cool completely.
For the Key Lime Ice Cream:
Process cream in blender until soft peaks form, 20 to 30 seconds. Scrape down sides of blender jar and continue to process until stiff peaks form, about 10 seconds longer. Using rubber spatula, stir in condensed milk, limeade concentrate, buttermilk, corn syrup, sugar, and salt. Process until thoroughly combined, about 20 seconds, scraping down sides of blender jar as needed.
Pour cream mixture evenly among 12 – 4 oz jelly jars (we like these). Spoon about 1 ½ tablespoons of the graham cracker crumbles on top of each and top with lids. Freeze until firm, at least 4 hours. Top with whipped cream if desired and enjoy!
The sealed jars keep well in the freezer for several months.