Line a rimmed baking sheet (about 10×15 inches) with parchment paper or aluminum foil. Lightly spray with nonstick spray if needed so the bark releases easily. Spread the mini pretzels in an even layer over the lined pan. Aim for mostly a single layer; a few small gaps are fine.

If you’re doing the brief oven bake, preheat your oven to 350°F (175°C) while you prepare the caramel.

In a medium heavy-bottomed saucepan, add the unsalted butter and packed light brown sugar. Heat over medium heat, stirring gently as the butter melts and combines with the sugar until the mixture is smooth.

Let the mixture come to a steady, gentle boil. Once bubbling, cook for 3–5 minutes, stirring often, until it thickens slightly and turns a rich amber color and starts to pull away from the sides of the pan. If using a candy thermometer, you’re aiming for about 235–245°F (soft-ball stage).

Turn the heat down to low. Carefully stir in the heavy cream, vanilla extract, and fine sea salt. The caramel will bubble up; stir gently until it becomes smooth again. If it looks separated or oily, keep stirring over low heat for 30–60 seconds until it comes back together.

Immediately and carefully pour the hot caramel over the pretzel layer, trying to cover as evenly as possible. Use a heatproof spatula to nudge the caramel toward the corners. Work fairly quickly, as the caramel will begin to set as it cools.

Place the tray with pretzels and caramel into the preheated oven and bake at 350°F (175°C) for 5–7 minutes, until the caramel is bubbling all over and slightly thicker but not dark or smoking. Remove from the oven and let it sit for 2–3 minutes so it’s very hot but not aggressively bubbling. For a no-oven version, skip this bake and instead let the caramel-covered pretzels rest at room temperature for 5–10 minutes.

While the caramel layer is baking or resting, melt the chocolate chips with 1 teaspoon neutral oil. For the microwave method: place chocolate chips and oil in a microwave-safe bowl and heat in 20-second bursts, stirring between each, until just melted and smooth. For a double boiler: place a heatproof bowl over a pot of gently simmering water (without the bowl touching the water) and stir the chocolate and oil until smooth.

Pour the melted chocolate over the hot caramel-covered pretzels. Use an offset spatula or the back of a spoon to spread it into an even, smooth layer from edge to edge.

Melt the white chocolate chips with a tiny drizzle of neutral oil using the same method as before. Drizzle the melted white chocolate in thin lines across the darker chocolate layer, then use a toothpick or the tip of a knife to gently drag through the lines to create swirls.

While the chocolate is still wet, sprinkle the top with flaky sea salt. Add any desired toppings such as chopped pecans or almonds, toffee bits, or extra crushed pretzels for added crunch and texture.

Place the pan in the refrigerator for 1–2 hours, or until the bark is completely firm. For a faster set, chill in the freezer for about 30–45 minutes.

Once fully set, lift the sheet of bark out of the pan using the parchment or foil. Use a sharp knife to cut into squares or break it into rustic shards with your hands. Serve or package for gifting.