If using a salt rim, run a wedge of lime around half the rim of your glass and dip it into flaky sea salt mixed.
Add the tequila, Cointreau, lime juice, lemon juice, mandarin juice, marmalade, orange bitters (if using) and a small pinch of flaky salt to a cocktail shaker filled with ice.
Shake vigorously for 15–20 seconds until the marmalade has fully dissolved and the cocktail is well chilled.
Double strain into a rocks glass over fresh ice.
Express the oils from an orange peel over the drink, rub it around the rim of the glass and drop it in. Garnish with a thin mandarin wheel.