public static BlockHeaderBuilder createDefault() {
    return new BlockHeaderBuilder()
        .parentHash(Hash.EMPTY)
        .coinbase(Address.ZERO)
        .difficulty(Difficulty.ONE)
        .number(0)
        .gasLimit(30_000_000)
        .timestamp(0)
        .ommersHash(Hash.EMPTY_LIST_HASH)
        .stateRoot(Hash.EMPTY_TRIE_HASH)
        .transactionsRoot(Hash.EMPTY)
        .receiptsRoot(Hash.EMPTY)
        .logsBloom(LogsBloomFilter.empty())
        .gasUsed(0)
        .extraData(Bytes.EMPTY)
        .mixHash(Hash.EMPTY)
        .nonce(0)
        .blobGasUsed(0L)
        .excessBlobGas(BlobGas.ZERO)
        .blockHeaderFunctions(new MainnetBlockHeaderFunctions());
  }
A utility class for building block headers.
ethereum/core/src/main/java/org/hyperledger/besu/ethereum/core/BlockHeaderBuilder.java