Warm the honey over medium-low heat just until loosened. Stir in the baking soda and cook, whisking, until the mixture darkens slightly and bubbles. Add the butter and salt, stirring until melted. Remove from heat and cool.

Whisk the eggs and sugar until pale and airy. Fold in the cooled honey mixture, then add the flour to form a soft dough.

Line two 15-by-17-inch/38-by-42-centimeter baking sheets with parchment. Spread half the dough on each sheet. Bake one at a time at 355°F/180°C convection until golden, 5 to 7 minutes. Do not overbake. Cool completely.

Whip the softened butter with dulce de leche until smooth and creamy.

Trim the edges of the baked sheets. Reserve scraps. Cut each sheet into 4 equal rectangles, yielding 8 layers.

Assemble the cake by alternating cake and cream until all 8 layers are stacked. Spread cream over the top and sides. Grind the scraps into fine crumbs and press them onto the cake.

Refrigerate at least 2 hours before serving. Store airtight in the refrigerator for up to 2 weeks.