List of Records to Row - API

See the following M code, which you need to put in a blank query. 

1) In Power Query, select New Source, then Blank Query
2) On the Home ribbon, select "Advanced Editor" button
3) Remove everything you see, then paste the M code I've given you in that box.
4) Press Done

let
    Source = 0,
    #"Converted to Table" = #table(1, {{Source}}),
    #"Added Custom" = Table.AddColumn(#"Converted to Table", "Custom", each {[A = 1, B = 2],[A = 4, B = 8]}),
    #"Expanded Custom" = Table.ExpandListColumn(#"Added Custom", "Custom"),
    #"Expanded Custom1" = Table.ExpandRecordColumn(#"Expanded Custom", "Custom", {"A", "B"}, {"A", "B"}),
    #"Unpivoted Other Columns" = Table.UnpivotOtherColumns(#"Expanded Custom1", {"Column1"}, "Attribute", "Value")
in
    #"Unpivoted Other Columns"

Turns this:

Into this

Which I then expand and unpivot to get this:

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