Place nuts in a food processor; process until ground. With processor on, drizzle oil through food chute; process 30 seconds or until almost smooth. Combine almond mixture, sugars, and butter in a bowl; beat with a mixer at medium speed 1 minute or until well blended. Add vanilla and egg; beat to combine. Weigh or lightly spoon flour into a dry measuring cup; level with a knife. Combine flour, rosemary, baking soda, and 1/8 teaspoon fleur de sel. Add flour mixture to sugar mixture; beat at low speed just until combined. Chill 15 minutes.
Preheat oven to 375°.
Divide dough into 24 portions (2 teaspoons each); roll each into a ball. Arrange 12 balls on each of 2 baking sheets lined with parchment paper. Flatten each into a 1 1/2-inch circle. Sprinkle 12 circles with remaining 1/4 teaspoon fleur de sel, pressing gently to adhere. Bake at 375° for 9 minutes or until lightly browned. Cool on wire rack.
Turn 12 unsalted cookies upside down; spread about 2 1/2 tablespoons ice cream over each. Top with 12 salted cookies. Freeze 2 hours or until firm.