In large bowl, melt butter and chocolate in microwave for 5 minutes, or in pan on stove over low heat (if in pan, stir constantly). Stir until completely melted. Add sugar and mix til sugar is absorbed by chocolate. Add eggs and vanilla and stir, then add flour and stir til lumps are gone, don't stir more than that. Mix in nuts. Pour thin layer of batter into greased 8x12 pan (just enough to cover the bottom). Melt carmel in microwave for 30 seconds, or in pan until soft. The carmel will still be in squares, but it will be warm and soft. With fingers, flatten squares into larger squares and put on top of brownie layer. Add the rest of the batter. Bake at 180ºC or 35 to 40 minutes.