Combine pretzel crumbs, melted butter, and brown sugar in a medium bowl.

Press the mixture into a 10-inch diameter pie plate.

Refrigerate the crust until firm.

Place 1 tbsp lime juice in a small bowl and sprinkle gelatin over it to bloom.

Combine remaining lime juice, egg yolks, 10 tbsp sugar, tequila, lime zest, and salt in a heavy medium saucepan.

Bring the mixture to a simmer over medium-low heat, stirring constantly to prevent scorching.

Remove the saucepan from the heat and add the bloomed gelatin. Stir until completely dissolved.

Pour the lime mixture into a medium bowl.

Place the bowl in a larger bowl filled with ice water and cool until the mixture becomes syrupy, stirring occasionally.

In another medium bowl, beat egg whites and 3 tbsp sugar until stiff, but not dry, peaks form.

In a large bowl, whip 1/2 cup chilled cream until soft peaks form.

Mix 1/4 of the cooled lime mixture into the whipped cream to lighten it.

Gently fold in the remaining lime mixture.

Fold in the beaten egg whites, being careful not to deflate the mixture.

Pour the filling into the prepared pretzel crust.

Refrigerate the pie until set, at least 2 hours.

Spread the remaining whipped cream (1/2 cup, beaten to soft peaks) atop the pie.

Garnish with lime slices and serve chilled.