Preparation

Make the chocolate-hazelnut spread

• Preheat the oven to 350°F. Arrange the hazelnuts on a rimmed baking sheet and toast, shaking the pan halfway through roasting, until golden brown, 12 to15 minutes. Transfer the hazelnuts to a heat-safe plate to cool. (If the hazelnuts are skin-on, wrap them in a tea towel, set aside for a minute, then use the towel to rub off the skins.) Once cool, transfer the nuts to a food processor and grind until they become a smooth paste, scraping down the bowl as needed, about 1 to 3 minutes.
• Add the sugar, honey, confectioners’ sugar, oil, and salt to the nut butter and blend until combined. Add the melted chocolate and process until combined, then scrape the mixture into an airtight container and leave out at room temperature to thicken for about 3 hours or overnight.

Make the toast

• Spread the bread slices with the butter and sprinkle with salt. Drizzle one side of each slice of bread with oil (olive oil or grapseed oils are my go-to selects). Position an oven rack in the top third of the oven, 3 to 4 inches from the broiler element and preheat to high. Set the bread on a foil lined baking sheet and broil until golden brown, about 2to 3 minutes. Flip the bread slices and toast to the other side until golden brown, another 1 to 2 minutes.
• Remove from the broiler and swipe some chocolate-hazelnut spread over each slice. Top with a handful of marshmallows. Position an oven rack in the top third of the oven, then return the baking sheet to the broiler. Broil the toasts until the marshmallows are golden brown, 15 to 30 seconds (watch the marshmallows closely as broiler intensities vary). Let cool for 1 to 2 minutes before serving.

Make Ahead Tips

The spread can be refrigerated after 1 day for up to 2 weeks; let it sit out at room temperature for at least 30 minutes before using so it returns to a spreadable consistency. Note that after refrigerating, the texture will be less smooth.