remix-project/libs/remix-simulator/src/genesis.ts

import { Block, BlockHeader } from '@ethereumjs/block'
import { BN } from 'ethereumjs-util'

export function generateBlock (executionContext) {
  const header: BlockHeader = BlockHeader.fromHeaderData({
    timestamp: (new Date().getTime() / 1000 | 0),
    number: 0,
    coinbase: '0x0e9281e9c6a0808672eaba6bd1220e144c9bb07a',
    difficulty: new BN('69762765929000', 10),
    gasLimit: new BN('8000000').imuln(1)
  })
  const block: Block = new Block(header, [], [])

  executionContext.vm().runBlock({ block: block, generate: true, skipBlockValidation: true, skipBalance: false }).then(() => {
    executionContext.addBlock(block)
  })
}