Step 1

Brush a 9-by-5-inch loaf pan with oil and line with parchment, leaving a 2-inch overhang on long sides.

Step 2

In a food processor, pulse 1 1/2 cups walnuts, dates, peanut butter, vanilla, and kosher salt until finely chopped and mixture holds together. Transfer to a parchment-lined baking sheet and lightly knead to pack together; pat into an 8-inch square. Refrigerate until firm, 20 minutes.

Step 3

Meanwhile, melt chocolate with oil. Halve nut mixture and press one part into loaf pan. Drizzle with half of chocolate. Refrigerate until chocolate just begins to set, 10 minutes.

Step 4

Press in remaining nut mixture and spread with remaining chocolate. Sprinkle with remaining 1/4 cup walnuts and flaky salt. Refrigerate until firm, at least 2 hours. To serve, let stand at room temperature 10 minutes, then remove from pan using parchment before slicing.