How to Make It
Preheat the oven to 300° and line a baking sheet with parchment paper. In a standing mixer fitted with the paddle, beat the butter with the sugar, honey, vanilla and salt until smooth. Add the flour, oats and baking soda and beat at low speed until a stiff batter forms.
Using an offset spatula, spread the batter onto the parchment in a rough rectangle 1/4 inch thick. Bake in the center of the oven for 15 minutes, until lightly golden. Reduce the oven temperature to 200° and bake until deeply golden and firm, about 40 minutes longer. Let cool completely, then break the crumble into pieces.
Line a large baking sheet with parchment paper. In a small saucepan, combine the sugar, butter, honey and salt with 1⁄4 cup of water. Bring to a boil, washing down any crystals from the side of the pan with a moistened pastry brush. Cook over moderately high heat, without stirring, until the syrup reaches 300° on a candy thermometer, about 10 minutes. Remove from the heat. Stir in the baking soda and immediately pour the mixture onto the parchment paper in a thin layer without disturbing the bubbles. Let the honey brittle cool completely, then break into shards.
Sprinkle some of the honey brittle into bowls and top with scoops of ice cream. Drizzle with buckwheat honey and garnish with the honey-oat crumble.