Melt the butter in a skillet or small saucepan over medium heat. Let it brown until nutty and fragrant, about 3 to 4 minutes, then remove from heat and set aside.
In another saucepan, heat the cream, milk, and ⅔ cup maple syrup over medium-low heat until steaming.
While the cream heats, whisk the egg yolks in a bowl until smooth.
Stream about half of the heated milk mixture into the eggs, whisking constantly, until incorporated.
Add the tempered eggs into the saucepan with the remaining cream mixture.
Cook over medium-low heat until mixture forms a custard and coats the back of a spatula, about 3 to 4 minutes. Stir constantly and do not allow to boil.
Remove from the heat and stir in the vanilla and salt.
Using an immersion blender, begin blending the custard in the saucepan on low speed. Stream in the slightly cooled browned butter to incorporate.
Refrigerate the custard until completely chilled, about 4 hours or up to overnight.
In the meantime, make the pecan clusters. Toast the pecans in a dry skillet over medium heat, about 3 minutes, stirring constantly.
Add 2 tablespoons maple syrup, brown sugar, and a pinch of salt. Cook until the sugar dissolves and the pecans are glazed.
Spread the pecans onto a parchment-lined sheet tray and cool until hardened.
Transfer the custard to an ice cream maker and churn for 15 to 20 minutes, until thick but still churning.
Fold in the pecans and continue churning until the ice cream is very thick.
Serve the ice cream right away for a softer consistency, or transfer to a freezer-safe container and freeze until ready to serve.